Error correction method and reproduction apparatus

ABSTRACT

A reproduction method includes a step of performing error correction of the first coded data piece and generating error location information which represents an error location of the first coded data; a step of generating erasure locator information which represents an erasure position of the second coded data piece, based on the error location information; and an erasure error correction step of performing erasure error correction of the second coded data piece based on the erasure locator information. The erasure locator information generation step includes the step of, when the error location information indicates that no error is detected in the Nth first symbol and the (N+2)th first symbol and that an error is detected in the (N+1)th first symbol, determining at least one of the plurality of second symbols provided adjacent to the (N+1)th first symbol as representing erasure.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an error correction method forcorrecting an error of composite coded data having at least one secondsymbol between first symbols forming first coded data which iserror-correction-coded using a first error correction code, betweensynchronization data pieces for synchronizing data, or between the firstsymbol and the synchronization data, the second symbol forming secondcoded data which is error-correction-coded using a second errorcorrection code having a lower degree of redundancy than the first errorcorrection code. The present invention also relates to a reproductionapparatus for carrying out such an error correction method.

[0003] 2. Description of the Related Art

[0004] Optical discs which are representative recording mediums haverecently increased in density and capacity, and thus require improvedreliability. Various error correction methods for correcting errorscaused by defects of a recording medium itself or dust or scratches onthe recording medium have been proposed (for example, U.S. Pat. No.6,367,049B1, pages 5 to 6 and FIG. 5; and Japanese National-Phase PCTLaid-Open Publication No. 2001-515642, pages 10 to 11 and FIG. 2).

[0005]FIG. 2 shows an exemplary composite coded data piece 203, togetherwith a first coded data piece 201 and a second coded data piece 202.With reference to FIG. 2, an error correction method will be described.

[0006] The composite coded data piece 203 includes first coded datapieces 206, 207, 208, 209, 210 and 211 which have beenerror-correction-coded using a first error correction code; and secondcoded data pieces 212, 213, 214, 215, 216, 217, 218 and 219 which havebeen error-correction-coded using a second error correction code havinga lower degree of redundancy than the first error correction code. Thecomposite coded data piece 203 also includes synchronization data pieces204 and 205 for synchronizing the first coded data piece and the secondcoded data piece.

[0007] The first coded data piece 201 is error-corrected using 24 firsterror correction codes. The second coded data piece 202 iserror-correction-coded using 304 second error correction codes. Thefirst coded data piece 201 is divided into the plurality of first codeddata pieces 206 through 211. The second coded data piece 202 is dividedinto the plurality of second coded data pieces 212 through 219. Thefirst coded data pieces 206 through 211 each include a plurality offirst symbols, and the second coded data pieces 212 through 219 eachinclude a plurality of second symbols.

[0008] Between two adjacent synchronization data pieces, among aplurality of synchronization data pieces, at least one first coded datapiece is provided. For example, as shown in FIG. 2, the first coded datapieces 206 through 208 including the first symbols are arranged betweentwo adjacent synchronization data pieces 204 and 205. Thus, at least onefirst symbol is provided between two adjacent synchronization datapieces.

[0009] Between the synchronization data piece and the first coded datapiece, at least one second coded data piece is provided. Between twoadjacent first coded data pieces, at least one second coded data pieceis provided. For example, as shown in FIG. 2, the second coded datapiece 212 is provided between the synchronization data piece 204 and thefirst coded data piece 206. The second coded data piece 213 is providedbetween two adjacent first coded data pieces 206 and 207. Thus, at leastone second symbol is provided between the synchronization data piece andthe first symbol, and between two first symbols. In FIG. 2, 38 secondsymbols are arranged between two first symbols adjacent to each other ina recording direction 220. 38 second symbols are arranged between thesynchronization data piece and the first symbol adjacent to each otherin the recording direction 220.

[0010] The first coded data piece 201 and the second coded data piece202 are respectively divided into the first coded data pieces 206through 211 and the second coded data pieces 212 through 219 and thusarranged, such that local error areas on a recording medium aredispersed in the composite coded data piece 203. (Hereinafter, such aprocess of arranging the data in a dispersed manner will be referred toas “interleaving”.)

[0011] On the recording medium, the above-described composite coded datapieces 203 are arranged in the recording direction 220.

[0012] The first error correction code is a Reed Solomon code over anextension field obtained by adding root a of the primitive polynomial(expression 1) to a prime field GF(2), having 30 information bytes and32 parity bytes. The second error correction code is a Reed Solomon codeover an extension field obtained by adding root a of the primitivepolynomial (expression 1) to a prime field GF(2), having 216 informationbytes and 32 parity bytes.

x ⁸ +x ⁴ +x ³ +x ²+1=0  expression 1

[0013]FIG. 3 shows a flowchart 30 illustrating an error correctionmethod of the composite corrected data piece 203.

[0014] In step 301, the first coded data piece 201 is error-corrected.At this point, the first coded data piece 201 is subjected tode-interleaving, which is the opposite transform to interleaving.

[0015] In step 302, erasure locator information, which indicates aposition of erasure in the second coded data piece 202, is generated.The erasure locator information can be generated by, for example, one ofthe following three methods.

[0016]FIGS. 4 through 6 show the state of the synchronization datapieces or the first symbols when the second coded data piece isdetermined to represent erasure. In FIGS. 4 through 6, mark “X”represents that no synchronization data piece is detected or that thefirst symbol is incorrect. Mark “◯” represents that synchronization datais detected or that the first symbol is correct. FIGS. 4 through 6 showa portion of the data corresponding to one row (or a plurality of rows),in the recording direction, of the composite corrected data piece 203which is arranged in rows and columns.

[0017] With reference to FIG. 4, method 1 will be described. When, asshown in FIG. 4, the detection states of both the synchronization datapieces 401 and 402 which are adjacent to each other along a recordingdirection 404 (synchronization data pieces 401 and 402 maybe firstsymbols) are “X”, a second coded data piece 403 between thesynchronization data pieces 401 and 402 is determined to representerasure. Thus, erasure locator information representing such adetermination result is generated.

[0018] With reference to FIG. 5, method 2 will be described. When, asshown in FIG. 5, the detection state of the synchronization data pieces501, 502 and 503 which are consecutive in a recording direction 506(synchronization data pieces 501, 502 and 503 may be first symbols) is“X◯X”, the second coded data piece 504 between the synchronization datapieces 501 and 502, and the second coded data piece 505 between thesynchronization data pieces 502 and 503, are determined to representerasure. Thus, erasure locator information representing such adetermination result is generated.

[0019] With reference to FIG. 6, method 3 will be described. When, asshown in FIG. 6, the detection states of three or more consecutive firstsymbols 602 through 604 between synchronization data pieces 601 and 605which are adjacent in a recording direction 610 (synchronization data601 and 605 may be first symbols) are “X”, the second coded data pieces606 through 609, including the second coded data piece 606 between thefirst symbol 602 and the synchronization data 601 (detection state: “◯”)and the second coded data piece 609 between the first symbol 604 and thesynchronization data 605 (detection state: “◯”), are determined torepresent erasure. Thus, erasure locator information representing such adetermination result is generated.

[0020] In step 303 (FIG. 3), erasure locator information generated instep 302 is used to perform erasure error correction of the second codeddata pieces in the range represented by expression 2.

ε+2ν≦32  expression 2

[0021] Here, ε is the number of erasure positions, and v is the numberof errors other than erasure.

[0022] By the above-described methods for generating erasure locatorinformation, a second coded data piece may become undesirablyuncorrectable. FIG. 7 is a partial enlarged view of the compositeencoded data piece 203, which shows an example of an error pattern bywhich the second coded data piece becomes uncorrectable.

[0023] Data pieces 701 through 703 are each a first coded data piece ora synchronization data piece. Data pieces 704 through 709 are partialdata pieces of the second coded data piece provided in the vicinity ofthe data piece 702. At the positions of marks “◯” and “X”, one of apartial synchronization data piece, a first symbol or a second symbol isprovided. In data pieces 701 through 703, mark “X” represents that nosynchronization data is detected or that the first symbol is incorrect.Mark “◯” represents that synchronization data is detected or that thefirst symbol is correct. In data pieces 704 through 709, mark “X”represents that the second symbol which has been read is incorrect, andthe other portions represent that the second symbol which has been readis correct.

[0024] It is assumed that the errors as shown in FIG. 7 occur. By theabove-described methods for generating erasure locator information, thesecond symbols, which are incorrect, are not all determined to representerasure. Since the second coded data is erasure-error-corrected in therange represented by expression 2, only up to 16 errors other thanerasure can be corrected. Therefore, the errors of the pattern as shownin FIG. 7 cannot be corrected.

[0025] By the above-mentioned methods for generating erasure locatorinformation, the state determination result of synchronization datapiece which is used for generating the erasure locator information iseither “detected” or “not detected”. When a synchronization data pieceis detected with a positional offset, the symbols positioned before sucha synchronization data piece are incorrect with a high probability, andthe symbols positioned after such a synchronization data piece arecorrect with a high probability. The reason is that the offset of thesynchronization is corrected by a reproduction apparatus, and thesymbols positioned after the synchronization data piece detected with apositional offset is read after the offset of synchronization iscorrected.

[0026] In the case where the state determination result ofsynchronization data piece is either “detected” or “not detected”, thefollowing occurs. When a synchronization data piece detected with apositional offset is determined to be “detected”, the symbols positionedbefore such a synchronization data piece may not be determined torepresent erasure, despite the fact that these symbols are incorrect. Asa result, the incorrect symbols may not be corrected. When asynchronization data piece detected with a positional offset isdetermined to be “not detected”, even the correct symbols positionedafter such a synchronization data piece may be determined to representerasure. In such a case, the number of erasure positions is increasedand the correction may become impossible.

SUMMARY OF THE INVENTION

[0027] According to one aspect of the invention, a reproduction methodfor reproducing a composite coded data piece from a recording mediumhaving the composite coded data piece recorded thereon is provided. Thecomposite coded data piece includes a first coded data piece which iserror-correction-coded using a first error correction code, and a secondcoded data piece which is error-correction-coded using a second errorcorrection code having a lower degree of redundancy than that of thefirst error correction code. The first coded data piece includes aplurality of first symbols. The second coded data piece includes aplurality of second symbols. At least one of the plurality of secondsymbols is provided between two adjacent first symbols of the pluralityof first symbols. The plurality of first symbols include an Nth firstsymbol, an (N+1)th first symbol and an (N+2)th first symbol, where N isan integer. The reproduction method includes a reading step of readingthe composite coded data piece from the recording medium and outputtingthe first coded data piece and the second coded data piece; an errorlocation information generation step of performing error correction ofthe first coded data piece and generating error location informationwhich represents an error location of the first coded data; an erasurelocator information generation step of generating erasure locatorinformation which represents an erasure position of the second codeddata piece, based on the error location information; and an erasureerror correction step of performing erasure error correction of thesecond coded data piece based on the erasure locator information. Theerasure locator information generation step includes the step of, whenthe error location information indicates that no error is detected inthe Nth first symbol and the (N+2)th first symbol and that an error isdetected in the (N+1)th first symbol, determining at least one of theplurality of second symbols provided adjacent to the (N+1)th firstsymbol as representing erasure.

[0028] In one embodiment of the invention, the erasure locatorinformation generation step further includes the step of, when the errorlocation information indicates that no error is detected in the Nthfirst symbol and the (N+2)th first symbol and that an error is detectedin the (N+1)th first symbol, determining at least one second symbolprovided adjacent to the (N+1)th first symbol, among at least one secondsymbol provided between the Nth first symbol and the (N+1)th firstsymbol as representing erasure; and determining at least one secondsymbol provided adjacent to the (N+1)th first symbol, among at least onesecond symbol provided between the (N+1)th first symbol and the (N+2)thfirst symbol as representing erasure.

[0029] In one embodiment of the invention, the erasure locatorinformation generation step further includes the step of, when the errorlocation information indicates that an error is detected in both of twoadjacent first symbols, determining all the second symbols providedbetween the two adjacent first symbols as representing erasure.

[0030] According to another aspect of the invention, a reproductionmethod for reproducing a composite coded data piece from a recordingmedium having the composite coded data piece recorded thereon isprovided. The composite coded data piece includes a first coded datapiece which is error-correction-coded using a first error correctioncode, and second coded data piece which is error-correction-coded usinga second error correction code having a lower degree of redundancy thanthat of the first error correction code. The first coded data pieceincludes a plurality of first symbols. The second coded data pieceincludes a plurality of second symbols. At least two of the plurality ofsecond symbols are provided between two adjacent first symbols of theplurality of first symbols. The reproduction method includes a readingstep of reading the composite coded data piece from the recording mediumand outputting the first coded data piece and the second coded datapiece; an error location information generation step of performing errorcorrection of the first coded data piece and generating error locationinformation which represents an error location of the first coded data;an erasure locator information generation step of generating erasurelocator information which represents an erasure position of the secondcoded data piece, based on the error location information; and anerasure error correction step of performing erasure error correction ofthe second coded data piece based on the erasure locator information.The erasure locator information generation step includes the step of,when the error location information indicates that a first symboldetected to have no error and a first symbol detected to have an errorare adjacent to each other, determining at least one second symbolprovided adjacent to the first symbol detected to have an error, amongat least two second symbols provided between the first symbol detectedto have no error and the first symbol detected to have an error, asrepresenting erasure: and determining at least one second symbolprovided adjacent to the first symbol detected to have no error as notrepresenting erasure.

[0031] In one embodiment of the invention, the erasure locatorinformation generation step further includes the step of, when the errorlocation information indicates that an error is detected in both of twoadjacent first symbols, determining all the second symbols providedbetween the two adjacent first symbols as representing erasure.

[0032] According to still another aspect of the invention, areproduction method for reproducing a coded data piece from a recordingmedium having a plurality of synchronization data pieces and the codeddata piece which is error-correction-coded recorded thereon is provided.The coded data piece includes a plurality of symbols. At least one ofthe plurality of symbols is provided between two adjacentsynchronization data pieces among the plurality of synchronization datapieces. The plurality of synchronization data pieces include an Nthsynchronization data piece, an (N+1)th synchronization data piece, andan (N+2)th synchronization data piece, where N is an integer. Thereproduction method includes a reading step of reading the plurality ofsynchronization data pieces and the coded data piece from the recordingmedium; a synchronization detection information generation step ofdetecting states of the plurality of synchronization data pieces andgenerating synchronization detection information which represents thedetection result: an erasure locator information generation step ofgenerating erasure locator information which represents an erasureposition of the coded data piece, based on the synchronization detectioninformation; and an erasure error correction step of performing erasureerror correction of the coded data piece based on the erasure locatorinformation. The erasure locator information generation step includesthe step of, when the synchronization detection information indicatesthat the Nth synchronization data piece and the (N+2)th synchronizationdata piece are detected and the (N+1)th synchronization data piece isnot detected, determining at least one of the plurality of symbolsprovided adjacent to the (N+1)th synchronization data piece asrepresenting erasure.

[0033] In one embodiment of the invention, the erasure locatorinformation generation step further includes the step of, when thesynchronization detection information indicates that the Nthsynchronization data piece and the (N+2)th synchronization data pieceare detected and the (N+1)th synchronization data piece is not detected,determining at least one symbol provided adjacent to the (N+1)thsynchronization data piece, among at least one symbol provided betweenthe Nth synchronization data piece and the (N+1)th synchronization datapiece as representing erasure; and determining at least one symbolprovided adjacent to the (N+1)th synchronization data piece, among atleast one symbol provided between the (N+1)th synchronization data pieceand the (N+2)th synchronization data piece as representing erasure.

[0034] In one embodiment of the invention, the erasure locatorinformation generation step further includes the step of, when thesynchronization detection information indicates that neither of the twoadjacent synchronization data pieces are detected, determining all thesymbols provided between the two undetected synchronization data piecesas representing erasure.

[0035] According to still another aspect of the invention, areproduction method for reproducing a coded data piece from a recordingmedium having a plurality of synchronization data pieces and the codeddata piece which is error-correction-coded recorded thereon is provided.The coded data piece includes a plurality of symbols. At least two ofthe plurality of symbols are provided between two adjacentsynchronization data pieces of the plurality of synchronization datapieces. The reproduction method includes a reading step of reading theplurality of synchronization data pieces and the coded data piece fromthe recording medium; a synchronization detection information generationstep of detecting states of the plurality of synchronization data piecesand generating synchronization detection information which representsthe detection result; an erasure locator information generation step ofgenerating erasure locator information which represents an erasureposition of the coded data piece, based on the synchronization detectioninformation; and an erasure error correction step of performing erasureerror correction of the coded data piece based on the erasure locatorinformation. The erasure locator information generation step includesthe step of, when the synchronization detection information indicatesthat a synchronization data piece adjacent to a detected synchronizationdata piece is not detected, determining at least one symbol adjacent tothe undetected synchronization data piece, among at least two symbolsprovided between the detected synchronization data piece and theundetected synchronization data piece, as representing erasure; anddetermining at least one symbol provided adjacent to the detectedsynchronization data piece as not representing erasure.

[0036] In one embodiment of the invention, the erasure locatorinformation generation step further includes the step of, when thesynchronization detection information indicates that neither of the twoadjacent synchronization data pieces are detected, determining all thesymbols provided between the two undetected synchronization data piecesas representing erasure.

[0037] According to still another aspect of the invention, areproduction method for reproducing a composite coded data piece from arecording medium having the composite coded data piece recorded thereonis provided. The composite coded data piece includes a first coded datapiece which is error-correction-coded using a first error correctioncode, a second coded data piece which is error-correction-coded using asecond error correction code having a lower degree of redundancy thanthat of the first error correction code, and a plurality ofsynchronization data pieces. The first coded data piece includes aplurality of first symbols. The second coded data piece includes aplurality of second symbols. At least one first symbol is providedbetween two adjacent synchronization data pieces among the plurality ofsynchronization data pieces. At least one of the plurality of secondsymbols is provided at least between a synchronization data piece and afirst symbol. The reproduction method includes a reading step of readingthe composite coded data piece from the recording medium and outputtingthe first coded data piece, the second coded data piece, and theplurality of synchronization data pieces; a synchronization detectioninformation generation step of detecting states of the plurality ofsynchronization data pieces and generating synchronization detectioninformation which represents the detection result; an error locationinformation generation step of performing error correction of the firstcoded data piece and generating error location information whichrepresents an error location of the first coded data; an erasure locatorinformation generation step of generating erasure locator informationwhich represents an erasure position of the second coded data piece,based on the error location information and the synchronizationdetection information; and an erasure error correction step ofperforming erasure error correction of the second coded data piece basedon the erasure locator information. The erasure locator informationgeneration step includes the step of, when the synchronization detectioninformation indicates that there is a synchronization data piece whichis not detected and the error location information indicates that noerror is detected in the first symbols immediately on both sides of theundetected synchronization data piece, determining at least one of theplurality of second symbols provided adjacent to the undetectedsynchronization data piece as representing erasure.

[0038] In one embodiment of the invention, at least two first symbolsare provided between two adjacent synchronization data pieces among theplurality of synchronization data pieces. At least one second symbol isprovided between two adjacent first symbols among the at least two firstsymbols. The erasure locator information generation step furtherincludes the step of, when the error location information indicates thatthere is a first symbol detected to have an error and at least one ofthe error location information and the synchronization detectioninformation indicates that one of a detected synchronization data pieceand a first symbol detected to have no error is immediately on each ofboth sides of the first symbol detected to have an error, determining atleast one of the plurality of second symbols provided adjacent to thefirst symbol detected to have an error as representing erasure.

[0039] According to still another aspect of the invention, areproduction method for reproducing a coded data piece from a recordingmedium having a plurality of synchronization data pieces and the codeddata piece which is error-correction-coded recorded thereon is provided.The coded data piece includes a plurality of symbols. At least one ofthe plurality of symbols is provided between two adjacentsynchronization data pieces among the plurality of synchronization datapieces. The plurality of synchronization data pieces include an Nthsynchronization data piece and an (N+1)th synchronization data piece,where N is an integer. The reproduction method includes a reading stepof reading the plurality of synchronization data pieces and the codeddata piece from the recording medium; a synchronization detectioninformation generation step of detecting states of the plurality ofsynchronization data pieces and generating synchronization detectioninformation which represents the detection result; an erasure locatorinformation generation step of generating erasure locator informationwhich represents an erasure position of the coded data piece, based onthe synchronization detection information; and an erasure errorcorrection step of performing erasure error correction of the coded datapiece based on the erasure locator information. The erasure locatorinformation generation step includes the step of, when thesynchronization detection information indicates that the (N+1)thsynchronization data piece is detected with a positional offset,determining at least one symbol provided between the Nth synchronizationdata piece and the (N+1)th synchronization data piece as representingerasure.

[0040] In one embodiment of the invention, the plurality ofsynchronization data pieces include an (N+2)th synchronization datapiece. The erasure locator information generation step further includesthe step of, when the synchronization detection information indicatesthat the (N+1)th synchronization data piece is detected with apositional offset, determining at least one symbol provided between the(N+1)th synchronization data piece and the (N+2)th synchronization datapiece as not representing erasure.

[0041] According to still another aspect of the invention, areproduction method for reproducing a composite coded data piece from arecording medium having the composite coded data piece recorded thereonis provided. The composite coded data piece includes a first coded datapiece which is error-correction-coded using a first error correctioncode, a second coded data piece which is error-correction-coded using asecond error correction code having a lower degree of redundancy thanthat of the first error correction code, and a plurality ofsynchronization data pieces. The first coded data piece includes aplurality of first symbols. The second coded data piece includes aplurality of second symbols. At least one first symbol is providedbetween two adjacent synchronization data pieces among the plurality ofsynchronization data pieces. At least one of the plurality of secondsymbols is provided at least between a synchronization data piece and afirst symbol. The plurality of synchronization data pieces include anNth synchronization data piece and an (N+1)th synchronization datapiece, where N is an integer. The reproduction method includes a readingstep of reading the composite coded data piece from the recording mediumand outputting the first coded data piece, the second coded data piece,and the plurality of synchronization data pieces; a synchronizationdetection information generation step of detecting states of theplurality of synchronization data pieces and generating synchronizationdetection information which represents the detection result; an errorlocation information generation step of performing error correction ofthe first coded data piece and generating error location informationwhich represents an error location of the first coded data; an erasurelocator information generation step of generating erasure locatorinformation which represents an erasure position of the second codeddata piece, based on the error location information and thesynchronization detection information; and an erasure error correctionstep of performing erasure error correction of the second coded datapiece based on the erasure locator information. The erasure locatorinformation generation step includes the step of, when thesynchronization detection information indicates that the (N+1)thsynchronization data piece is detected with a positional offset,determining at least one second symbol provided between the Nthsynchronization data piece and the (N+1)th synchronization data piece asrepresenting erasure.

[0042] In one embodiment of the invention, the plurality ofsynchronization data pieces include an (N+2)th synchronization datapiece. The erasure locator information generation step further includesthe step of, when the synchronization detection information indicatesthat the (N+1)th synchronization data piece is detected with apositional offset, determining at least one second symbol providedbetween the (N+1)th synchronization data piece and the (N+2)thsynchronization data piece as not representing erasure.

[0043] According to still another aspect of the invention, areproduction method for reproducing a composite coded data piece from arecording medium having the composite coded data piece recorded thereonis provided. The composite coded data piece includes a first coded datapiece which is error-correction-coded using a first error correctioncode, a second coded data piece which is error-correction-coded using asecond error correction code having a lower degree of redundancy thanthat of the first error correction code, and a plurality ofsynchronization data pieces. The first coded data piece includes aplurality of first symbols. The second coded data piece includes aplurality of second symbols. At least one first symbol is providedbetween two adjacent synchronization data pieces among the plurality ofsynchronization data pieces. At least one of the plurality of secondsymbols is provided at least between a synchronization data piece and afirst symbol. The plurality of synchronization data pieces include anNth synchronization data piece and an (N+1)th synchronization datapiece, where N is an integer. A prescribed first symbol is providedbetween the Nth synchronization data piece and the (N+1)thsynchronization data piece. The reproduction method includes a readingstep of reading the composite coded data piece from the recording mediumand outputting the first coded data piece, the second coded data piece,and the plurality of synchronization data pieces; a synchronizationdetection information generation step of detecting states of theplurality of synchronization data pieces and generating synchronizationdetection information which represents the detection result; an errorlocation information generation step of performing error correction ofthe first coded data piece and generating error location informationwhich represents an error location of the first coded data; an erasurelocator information generation step of generating erasure locatorinformation which represents an erasure position of the second codeddata piece, based on the error location information and thesynchronization detection information; and an erasure error correctionstep of performing erasure error correction of the second coded datapiece based on the erasure locator information. The erasure locatorinformation generation step includes the step of, when thesynchronization detection information indicates that the (N+1)thsynchronization data piece is detected with a positional offset,determining at least one second symbol provided between the prescribedfirst symbol and the (N+1)th synchronization data piece as representingerasure.

[0044] In one embodiment of the invention, the plurality ofsynchronization data pieces include an (N+2)th synchronization datapiece. Another prescribed first symbol is provided between the (N+1)thsynchronization data piece and the (N+2)th synchronization data piece.The erasure locator information generation step further includes thestep of, when the synchronization detection information indicates thatthe (N+1)th synchronization data piece is detected with a positionaloffset, determining at least one second symbol provided between the(N+1)th synchronization data piece and the another prescribed firstsymbol as not representing erasure.

[0045] According to still another aspect of the invention, areproduction method for reproducing a coded data piece from a recordingmedium having a plurality of synchronization data pieces and the codeddata piece which is error-correction-coded recorded thereon is provided.The coded data piece includes a plurality of symbols. At least one ofthe plurality of symbols is provided between two adjacentsynchronization data pieces of the plurality of synchronization datapieces. The reproduction method includes a reading step of reading theplurality of synchronization data pieces and the coded data piece fromthe recording medium; a synchronization detection information generationstep of detecting states of the plurality of synchronization data piecesand generating synchronization detection information which representsthe detection result; an erasure locator information generation step ofgenerating erasure locator information which represents an erasureposition of the coded data piece, based on the synchronization detectioninformation; and an erasure error correction step of performing erasureerror correction of the coded data piece based on the erasure locatorinformation. The erasure locator information generation step includesthe step of, when the synchronization detection information indicatesthat any two or more data pieces from undetected synchronization datapieces and synchronization data pieces detected with a positional offsetare consecutive, determining at least one symbol provided between theconsecutive synchronization data pieces as representing erasure.

[0046] According to still another aspect of the invention, areproduction method for reproducing a composite coded data piece from arecording medium having the composite coded data piece recorded thereonis provided. The composite coded data piece includes a first coded datapiece which is error-correction-coded using a first error correctioncode, a second coded data piece which is error-correction-coded using asecond error correction code having a lower degree of redundancy thanthat of the first error correction code, and a plurality ofsynchronization data pieces. The first coded data piece includes aplurality of first symbols. The second coded data piece includes aplurality of second symbols. At least one first symbol is providedbetween two adjacent synchronization data pieces among the plurality ofsynchronization data pieces. At least one of the plurality of secondsymbols is provided at least between a synchronization data piece and afirst symbol. The reproduction method includes a reading step of readingthe composite coded data piece from the recording medium and outputtingthe first coded data piece, the second coded data piece, and theplurality of synchronization data pieces; a synchronization detectioninformation generation step of detecting states of the plurality ofsynchronization data pieces and generating synchronization detectioninformation which represents the detection result; an error locationinformation generation step of performing error correction of the firstcoded data piece and generating error location information whichrepresents an error location of the first coded data; an erasure locatorinformation generation step of generating erasure locator informationwhich represents an erasure position of the second coded data piece,based on the error location information and the synchronizationdetection information; and an erasure error correction step ofperforming erasure error correction of the second coded data piece basedon the erasure locator information. The erasure locator informationgeneration step of, when the synchronization detection informationindicates that any two or more data pieces from undetectedsynchronization data pieces and synchronization data pieces detectedwith a positional offset are consecutive, determining at least onesecond symbol provided between the consecutive synchronization datapieces as representing erasure.

[0047] In one embodiment of the invention, the erasure locatorinformation generation step further includes the step of determining atleast one first symbol provided between the consecutive synchronizationdata pieces as representing erasure.

[0048] According to still another aspect of the invention, areproduction method for reproducing a composite coded data piece from arecording medium having the composite coded data piece recorded thereonis provided. The composite coded data piece includes a first coded datapiece which is error-correction-coded using a first error correctioncode, and a second coded data piece which is error-correction-codedusing a second error correction code having a lower degree of redundancythan that of the first error correction code. The first coded data pieceincludes a plurality of first symbols. The second coded data pieceincludes a plurality of second symbols. At least one of the plurality ofsecond symbols is provided between two adjacent first symbols of theplurality of first symbols. The reproduction method includes a readingstep of reading the composite coded data piece from the recording mediumand outputting the first coded data piece and the second coded datapiece; an error location information generation step of performing errorcorrection of the first coded data piece and generating error locationinformation which represents an error location of the first coded data;an erasure locator information generation step of generating at leastfirst erasure locator information and second erasure locator informationwhich represent an erasure position of the second coded data piece,based on the error location information; and an erasure error correctionstep of performing erasure error correction of the second coded datapiece based on at least one of the first erasure locator information andthe second erasure locator information. The erasure error correctionstep includes the step of, when there is an error which cannot becorrected based on the first erasure locator information, performingerasure error correction of the second coded data piece based on thesecond erasure locator information.

[0049] In one embodiment of the invention, the erasure locatorinformation generation step includes the steps of: when all the errorscan be corrected based on the first erasure locator information,generating erasure locator information for erasure error correction ofanother second coded data piece using an identical method as the methodused for generating the first erasure locator information, and when allthe errors can be corrected based on the second erasure locatorinformation, generating erasure locator information for erasure errorcorrection of another second coded data piece using an identical methodas the method used for generating the second erasure locatorinformation.

[0050] In one embodiment of the invention, the plurality of firstsymbols include an Nth first symbol, an (N+1)th first symbol and an(N+2)th first symbol, where N is an integer. The erasure locatorinformation generation step includes the step of, when the errorlocation information indicates that no error is detected in the Nthfirst symbol and the (N+2)th first symbol and that an error is detectedin the (N+1)th first symbol, determining at least one of the pluralityof second symbols provided adjacent to the (N+1)th first symbol asrepresenting erasure.

[0051] According to still another aspect of the invention, areproduction method for reproducing a coded data piece from a recordingmedium having a plurality of synchronization data pieces and the codeddata piece which is error-correction-coded recorded thereon is provided.The coded data piece includes a plurality of symbols. At least one ofthe plurality of symbols is provided between two adjacentsynchronization data pieces among the plurality of synchronization datapieces. The reproduction method includes a reading step of reading theplurality of synchronization data pieces and the coded data piece fromthe recording medium; a synchronization detection information generationstep of detecting states of the plurality of synchronization data piecesand generating synchronization detection information which representsthe detection result; an erasure locator information generation step ofgenerating at least first erasure locator information and second erasurelocator information which represent an erasure position of the codeddata piece, based on the synchronization detection information; and anerasure error correction step of performing erasure error correction ofthe coded data piece based on at least one of the first erasure locatorinformation and the second erasure locator information. The erasureerror correction step includes the step of, when there is an error whichcannot be corrected based on the first erasure locator information,performing erasure error correction of the coded data piece based on thesecond erasure locator information.

[0052] In one embodiment of the invention, the erasure locatorinformation generation step includes the steps of when all the errorscan be corrected based on the first erasure locator information,generating erasure locator information for erasure error correction ofanother coded data piece using an identical method as the method usedfor generating the first erasure locator information, and when all theerrors can be corrected based on the second erasure locator information,generating erasure locator information for erasure error correction ofanother coded data piece using an identical method as the method usedfor generating the second erasure locator information.

[0053] In one embodiment of the invention, the plurality ofsynchronization data pieces include an Nth synchronization data piece,an (N+1)th synchronization data piece, and an (N+2)th synchronizationdata piece, where N is an integer. The erasure locator informationgeneration step includes the step of, when the synchronization detectioninformation indicates that the Nth synchronization data piece and the(N+2)th synchronization data piece are detected and the (N+1)thsynchronization data piece is not detected, determining at least one ofthe plurality of symbols provided adjacent to the (N+1)thsynchronization data piece as representing erasure.

[0054] In one embodiment of the invention, the plurality ofsynchronization data pieces include an Nth synchronization data pieceand an (N+1)th synchronization data piece, where N is an integer. Theerasure locator information generation step includes the step of, whenthe synchronization detection information indicates that the (N+1)thsynchronization data piece is detected with a positional offset,determining at least one symbol provided between the Nth synchronizationdata piece and the (N+1)th synchronization data piece as representingerasure.

[0055] In one embodiment of the invention, the erasure locatorinformation generation step includes the step of, when thesynchronization detection information indicates that any two or moredata pieces from undetected synchronization data pieces andsynchronization data pieces detected with a positional offset areconsecutive, determining at least one symbol provided between theconsecutive synchronization data pieces as representing erasure.

[0056] According to still another aspect of the invention, areproduction method for reproducing a composite coded data piece from arecording medium having the composite coded data piece recorded thereonis provided. The composite coded data piece includes a first coded datapiece which is error-correction-coded using a first error correctioncode, a second coded data piece which is error-correction-coded using asecond error correction code having a lower degree of redundancy thanthat of the first error correction code, and a plurality ofsynchronization data pieces. The first coded data piece includes aplurality of first symbols. The second coded data piece includes aplurality of second symbols. At least one first symbol is providedbetween two adjacent synchronization data pieces among the plurality ofsynchronization data pieces. At least one of the plurality of secondsymbols is provided at least between a synchronization data piece and afirst symbol. The reproduction method includes a reading step of readingthe composite coded data piece from the recording medium and outputtingthe first coded data piece, the second coded data piece, and theplurality of synchronization data pieces; a synchronization detectioninformation generation step of detecting states of the plurality ofsynchronization data pieces and generating synchronization detectioninformation which represents the detection result; an error locationinformation generation step of performing error correction of the firstcoded data piece and generating error location information whichrepresents an error location of the first coded data; an erasure locatorinformation generation step of generating at least first erasure locatorinformation and second erasure locator information which represent anerasure position of the second coded data piece, based on the errorlocation information and the synchronization detection information; andan erasure error correction step of performing erasure error correctionof the second coded data piece based on at least one of the firsterasure locator information and the second erasure locator information.The erasure error correction step includes the step of, when there is anerror which cannot be corrected based on the first erasure locatorinformation, performing erasure error correction of the second codeddata piece based on the second erasure locator information.

[0057] In one embodiment of the invention, the erasure locatorinformation generation step includes the steps of: when all the errorscan be corrected based on the first erasure locator information,generating erasure locator information for erasure error correction ofanother second coded data piece using an identical method as the methodused for generating the first erasure locator information, and when allthe errors can be corrected based on the second erasure locatorinformation, generating erasure locator information for erasure errorcorrection of another second coded data piece using an identical methodas the method used for generating the second erasure locatorinformation.

[0058] In one embodiment of the invention, the erasure locatorinformation generation step includes the steps of, when thesynchronization detection information indicates that there is asynchronization data piece which is not detected and the error locationinformation indicates that no error is detected in the first symbolsimmediately on both sides of the undetected synchronization data piece,determining at least one of the plurality of second symbols providedadjacent to the undetected synchronization data piece as representingerasure.

[0059] In one embodiment of the invention, at least two first symbolsare provided between two adjacent synchronization data pieces among theplurality of synchronization data pieces. At least one second symbol isprovided between two adjacent first symbols among the at least two firstsymbols. The erasure locator information generation step includes thestep of, when the error location information indicates that there is afirst symbol detected to have an error and at least one of the errorlocation information and the synchronization detection informationindicates that one of a detected synchronization data piece and a firstsymbol detected to have no error is immediately on each of both sides ofthe first symbol detected to have an error, determining at least one ofthe plurality of second symbols provided adjacent to the first symboldetected to have an error as representing erasure.

[0060] In one embodiment of the invention, the plurality ofsynchronization data pieces include an Nth synchronization data pieceand an (N+1)th synchronization data piece, where N is an integer. Theerasure locator information generation step includes the step of, whenthe synchronization detection information indicates that the (N+1)thsynchronization data piece is detected with a positional offset,determining at least one second symbol provided between the Nthsynchronization data piece and the (N+1)th synchronization data piece asrepresenting erasure.

[0061] In one embodiment of the invention, the erasure locatorinformation generation step includes the step of, when thesynchronization detection information indicates that any two or moredata pieces from undetected synchronization data pieces andsynchronization data pieces detected with a positional offset areconsecutive, determining at least one second symbol provided between theconsecutive synchronization data pieces as representing erasure.

[0062] According to still another aspect of the invention, areproduction apparatus for reproducing a composite coded data piece froma recording medium having the composite coded data piece recordedthereon is provided. The composite coded data piece includes a firstcoded data piece which is error-correction-coded using a first errorcorrection code, and a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code.The first coded data piece includes a plurality of first symbols. Thesecond coded data piece includes a plurality of second symbols. At leastone of the plurality of second symbols is provided between two adjacentfirst symbols of the plurality of first symbols. The plurality of firstsymbols include an Nth first symbol, an (N+1)th first symbol and an(N+2)th first symbol, where N is an integer. The reproduction apparatusincludes a reading section for reading the composite coded data piecefrom the recording medium and outputting the first coded data piece andthe second coded data piece; an error location information generationsection for performing error correction of the first coded data pieceand generating error location information which represents an errorlocation of the first coded data; an erasure locator informationgeneration section for generating erasure locator information whichrepresents an erasure position of the second coded data piece, based onthe error location information; and an erasure error correction sectionfor performing erasure error correction of the second coded data piecebased on the erasure locator information. When the error locationinformation indicates that no error is detected in the Nth first symboland the (N+2)th first symbol and that an error is detected in the(N+1)th first symbol, the erasure locator information generation sectiondetermines at least one of the plurality of second symbols providedadjacent to the (N+1)th first symbol as representing erasure.

[0063] In one embodiment of the invention, when the error locationinformation indicates that no error is detected in the Nth first symboland the (N+2)th first symbol and that an error is detected in the(N+1)th first symbol, the erasure locator information generation sectiondetermines at least one second symbol provided adjacent to the (N+1)thfirst symbol, among at least one second symbol provided between the Nthfirst symbol and the (N+1)th first symbol as representing erasure; anddetermining at least one second symbol provided adjacent to the (N+1)thfirst symbol, among at least one second symbol provided between the(N+1)th first symbol and the (N+2)th first symbol as representingerasure.

[0064] In one embodiment of the invention, when the error locationinformation indicates that an error is detected in both of two adjacentfirst symbols, the erasure locator information generation sectiondetermines all the second symbols provided between the two adjacentfirst symbols as representing erasure.

[0065] According to still another aspect of the invention, areproduction apparatus for reproducing a composite coded data piece froma recording medium having the composite coded data piece recordedthereon is provided. The composite coded data piece includes a firstcoded data piece which is error-correction-coded using a first errorcorrection code, and a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code.The first coded data piece includes a plurality of first symbols. Thesecond coded data piece includes a plurality of second symbols. At leasttwo of the plurality of second symbols are provided between two adjacentfirst symbols of the plurality of first symbols. The reproductionapparatus includes a reading section for reading the composite codeddata piece from the recording medium and outputting the first coded datapiece and the second coded data piece; an error location informationgeneration section for performing error correction of the first codeddata piece and generating error location information which represents anerror location of the first coded data; an erasure locator informationgeneration section for generating erasure locator information whichrepresents an erasure position of the second coded data piece, based onthe error location information; and an erasure error correction sectionfor performing erasure error correction of the second coded data piecebased on the erasure locator information. When the error locationinformation indicates that a first symbol detected to have no error anda first symbol detected to have an error are adjacent to each other, theerasure locator information generation section determines at least onesecond symbol provided adjacent to the first symbol detected to have anerror, among at least two second symbols provided between the firstsymbol detected to have no error and the first symbol detected to havean error, as representing erasure; and determines at least one secondsymbol provided adjacent to the first symbol detected to have no erroras not representing erasure.

[0066] In one embodiment of the invention, when the error locationinformation indicates that an error is detected in both of two adjacentfirst symbols, the erasure locator information generation sectiondetermines all the second symbols provided between the two adjacentfirst symbols as representing erasure.

[0067] According to still another aspect of the invention, areproduction apparatus for reproducing a coded data piece from arecording medium having a plurality of synchronization data pieces andthe coded data piece which is error-correction-coded recorded thereon isprovided. The coded data piece includes a plurality of symbols. At leastone of the plurality of symbols is provided between two adjacentsynchronization data pieces among the plurality of synchronization datapieces. The plurality of synchronization data pieces include an Nthsynchronization data piece, an (N+1)th synchronization data piece, andan (N+2)th synchronization data piece, where N is an integer. Thereproduction apparatus includes a reading section for reading theplurality of synchronization data pieces and the coded data piece fromthe recording medium; a synchronization detection information generationsection for detecting states of the plurality of synchronization datapieces and generating synchronization detection information whichrepresents the detection result; an erasure locator informationgeneration section for generating erasure locator information whichrepresents an erasure position of the coded data piece, based on thesynchronization detection information; and an erasure error correctionsection for performing erasure error correction of the coded data piecebased on the erasure locator information. When the synchronizationdetection information indicates that the Nth synchronization data pieceand the (N+2)th synchronization data piece are detected and the (N+1)thsynchronization data piece is not detected, the erasure locatorinformation generation section determines at least one of the pluralityof symbols provided adjacent to the (N+1)th synchronization data pieceas representing erasure.

[0068] In one embodiment of the invention, when the synchronizationdetection information indicates that the Nth synchronization data pieceand the (N+2)th synchronization data piece are detected and the (N+1)thsynchronization data piece is not detected, the erasure locatorinformation generation section determines at least one symbol providedadjacent to the (N+1)th synchronization data piece, among at least onesymbol provided between the Nth synchronization data piece and the(N+1)th synchronization data piece as representing erasure; anddetermines at least one symbol provided adjacent to the (N+1)thsynchronization data piece, among at least one symbol provided betweenthe (N+1)th synchronization data piece and the (N+2)th synchronizationdata piece as representing erasure.

[0069] In one embodiment of the invention, when the synchronizationdetection information indicates that neither of the two adjacentsynchronization data pieces are detected, the erasure locatorinformation generation section determines all the symbols providedbetween the two undetected synchronization data pieces as representingerasure.

[0070] According to still another aspect of the invention, areproduction apparatus for reproducing a coded data piece from arecording medium having a plurality of synchronization data pieces andthe coded data piece which is error-correction-coded recorded thereon isprovided. The coded data piece includes a plurality of symbols. At leasttwo of the plurality of symbols are provided between two adjacentsynchronization data pieces of the plurality of synchronization datapieces. The reproduction apparatus includes a reading section forreading the plurality of synchronization data pieces and the coded datapiece from the recording medium; a synchronization detection informationgeneration section for detecting states of the plurality ofsynchronization data pieces and generating synchronization detectioninformation which represents the detection result an erasure locatorinformation generation section for generating erasure locatorinformation which represents an erasure position of the coded datapiece, based on the synchronization detection information; and anerasure error correction section for performing erasure error correctionof the coded data piece based on the erasure locator information. Whenthe synchronization detection information indicates that asynchronization data piece adjacent to a detected synchronization datapiece is not detected, the erasure locator information generationsection determines at least one symbol provided adjacent to theundetected synchronization data piece, among at least two symbolsprovided between the detected synchronization data piece and theundetected synchronization data piece, as representing erasure; anddetermines at least one symbol provided adjacent to the detectedsynchronization data piece as not representing erasure.

[0071] In one embodiment of the invention, when the synchronizationdetection information indicates that neither of the two adjacentsynchronization data pieces are detected, the erasure locatorinformation generation section determines all the symbols providedbetween the two undetected synchronization data pieces as representingerasure.

[0072] According to still another aspect of the invention, areproduction apparatus for reproducing a composite coded data piece froma recording medium having the composite coded data piece recordedthereon is provided. The composite coded data piece includes a firstcoded data piece which is error-correction-coded using a first errorcorrection code, a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,and a plurality of synchronization data pieces. The first coded datapiece includes a plurality of first symbols. The second coded data pieceincludes a plurality of second symbols. At least one first symbol isprovided between two adjacent synchronization data pieces among theplurality of synchronization data pieces. At least one of the pluralityof second symbols is provided at least between a synchronization datapiece and a first symbol. The reproduction apparatus includes a readingsection for reading the composite coded data piece from the recordingmedium and outputting the first coded data piece, the second coded datapiece, and the plurality of synchronization data pieces; asynchronization detection information generation section for detectingstates of the plurality of synchronization data pieces and generatingsynchronization detection information which represents the detectionresult; an error location information generation section for performingerror correction of the first coded data piece and generating errorlocation information which represents an error location of the firstcoded data; an erasure locator information generation section forgenerating erasure locator information which represents an erasureposition of the second coded data piece, based on the error locationinformation and the synchronization detection information; and anerasure error correction section for performing erasure error correctionof the second coded data piece based on the erasure locator information.When the synchronization detection information indicates that there is asynchronization data piece which is not detected and the error locationinformation indicates that no error is detected in the first symbolsimmediately on both sides of the undetected synchronization data piece,the erasure locator information generation section determines at leastone of the plurality of second symbols provided adjacent to theundetected synchronization data piece as representing erasure.

[0073] In one embodiment of the invention, at least two first symbolsare provided between two adjacent synchronization data pieces among theplurality of synchronization data pieces. At least one second symbol isprovided between two adjacent first symbols among the at least two firstsymbols. When the error location information indicates that there is afirst symbol detected to have an error and at least one of the errorlocation information and the synchronization detection informationindicates that one of a detected synchronization data piece and a firstsymbol detected to have no error is immediately on each of both sides ofthe first symbol detected to have an error, the erasure locatorinformation generation section determines at least one of the pluralityof second symbols provided adjacent to the first symbol detected to havean error as representing erasure.

[0074] According to still another aspect of the invention, areproduction apparatus for reproducing a coded data piece from arecording medium having a plurality of synchronization data pieces andthe coded data piece which is error-correction-coded recorded thereon isprovided. The coded data piece includes a plurality of symbols. At leastone of the plurality of symbols is provided between two adjacentsynchronization data pieces among the plurality of synchronization datapieces. The plurality of synchronization data pieces include an Nthsynchronization data piece and an (N+1)th synchronization data piece,where N is an integer. The reproduction apparatus includes a readingsection for reading the plurality of synchronization data pieces and thecoded data piece from the recording medium; a synchronization detectioninformation generation section for detecting states of the plurality ofsynchronization data pieces and generating synchronization detectioninformation which represents the detection result; an erasure locatorinformation generation section for generating erasure locatorinformation which represents an erasure position of the coded datapiece, based on the synchronization detection information; and anerasure error correction section for performing erasure error correctionof the coded data piece based on the erasure locator information. Whenthe synchronization detection information indicates that the (N+1)thsynchronization data piece is detected with a positional offset, theerasure locator information generation section determines at least onesymbol provided between the Nth synchronization data piece and the(N+1)th synchronization data piece as representing erasure.

[0075] In one embodiment of the invention, the plurality ofsynchronization data pieces include an (N+2)th synchronization datapiece. When the synchronization detection information indicates that the(N+1)th synchronization data piece is detected with a positional offset,the erasure locator information generation section determines at leastone symbol provided between the (N+1)th synchronization data piece andthe (N+2)th synchronization data piece as not representing erasure.

[0076] According to still another aspect of the invention, areproduction apparatus for reproducing a composite coded data piece froma recording medium having the composite coded data piece recordedthereon is provided. The composite coded data piece includes a firstcoded data piece which is error-correction-coded using a first errorcorrection code, a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,and a plurality of synchronization data pieces. The first coded datapiece includes a plurality of first symbols. The second coded data pieceincludes a plurality of second symbols. At least one first symbol isprovided between two adjacent synchronization data pieces among theplurality of synchronization data pieces. At least one of the pluralityof second symbols is provided at least between a synchronization datapiece and a first symbol. The plurality of synchronization data piecesinclude an Nth synchronization data piece and an (N+1)th synchronizationdata piece, where N is an integer. The reproduction apparatus includes areading section for reading the composite coded data piece from therecording medium and outputting the first coded data piece, the secondcoded data piece, and the plurality of synchronization data pieces; asynchronization detection information generation section for detectingstates of the plurality of synchronization data pieces and generatingsynchronization detection information which represents the detectionresult; an error location information generation section for performingerror correction of the first coded data piece and generating errorlocation information which represents an error location of the firstcoded data; an erasure locator information generation section forgenerating erasure locator information which represents an erasureposition of the second coded data piece, based on the error locationinformation and the synchronization detection information; and anerasure error correction section for performing erasure error correctionof the second coded data piece based on the erasure locator information.When the synchronization detection information indicates that the(N+1)th synchronization data piece is detected with a positional offset,the erasure locator information generation section determines at leastone second symbol provided between the Nth synchronization data pieceand the (N+1) th synchronization data piece as representing erasure.

[0077] In one embodiment of the invention, the plurality ofsynchronization data pieces include an (N+2)th synchronization datapiece. When the synchronization detection information indicates that the(N+1)th synchronization data piece is detected with a positional offset,the erasure locator information generation section determines at leastone second symbol provided between the (N+1)th synchronization datapiece and the (N+2)th synchronization data piece as not representingerasure.

[0078] According to still another aspect of the invention, areproduction apparatus for reproducing a composite coded data piece froma recording medium having the composite coded data piece recordedthereon is provided. The composite coded data piece includes a firstcoded data piece which is error-correction-coded using a first errorcorrection code, a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,and a plurality of synchronization data pieces. The first coded datapiece includes a plurality of first symbols. The second coded data pieceincludes a plurality of second symbols. At least one first symbol isprovided between two adjacent synchronization data pieces among theplurality of synchronization data pieces. At least one of the pluralityof second symbols is provided at least between a synchronization datapiece and a first symbol. The plurality of synchronization data piecesinclude an Nth synchronization data piece and an (N+1)th synchronizationdata piece, where N is an integer. A prescribed first symbol is providedbetween the Nth synchronization data piece and the (N+1)thsynchronization data piece. The reproduction apparatus includes areading section for reading the composite coded data piece from therecording medium and outputting the first coded data piece, the secondcoded data piece, and the plurality of synchronization data pieces; asynchronization detection information generation section for detectingstates of the plurality of synchronization data pieces and generatingsynchronization detection information which represents the detectionresult; an error location information generation section for performingerror correction of the first coded data piece and generating errorlocation information which represents an error location of the firstcoded data; an erasure locator information generation section forgenerating erasure locator information which represents an erasureposition of the second coded data piece, based on the error locationinformation and the synchronization detection information; and anerasure error correction section for performing erasure error correctionof the second coded data piece based on the erasure locator information.When the synchronization detection information indicates that the(N+1)th synchronization data piece is detected with a positional offset,the erasure locator information generation section determines at leastone second symbol provided between the prescribed first symbol and the(N+1)th synchronization data piece as representing erasure.

[0079] In one embodiment of the invention, the plurality ofsynchronization data pieces include an (N+2)th synchronization datapiece. Another prescribed first symbol is provided between the (N+1)thsynchronization data piece and the (N+2)th synchronization data piece.When the synchronization detection information indicates that the(N+1)th synchronization data piece is detected with a positional offset,the erasure locator information generation section determines at leastone second symbol provided between the (N+1) th synchronization datapiece and the another prescribed first symbol as not representingerasure.

[0080] According to still another aspect of the invention, areproduction apparatus for reproducing a coded data piece from arecording medium having a plurality of synchronization data pieces andthe coded data piece which is error-correction-coded recorded thereon isprovided. The coded data piece includes a plurality of symbols. At leastone of the plurality of symbols is provided between two adjacentsynchronization data pieces of the plurality of synchronization datapieces. The reproduction apparatus includes a reading section forreading the plurality of synchronization data pieces and the coded datapiece from the recording medium; a synchronization detection informationgeneration section for detecting states of the plurality ofsynchronization data pieces and generating synchronization detectioninformation which represents the detection result; an erasure locatorinformation generation section for generating erasure locatorinformation which represents an erasure position of the coded datapiece, based on the synchronization detection information; and anerasure error correction section for performing erasure error correctionof the coded data piece based on the erasure locator information. Whenthe synchronization detection information indicates that any two or moredata pieces from undetected synchronization data pieces andsynchronization data pieces detected with a positional offset areconsecutive, the erasure locator information generation sectiondetermines at least one symbol provided between the consecutivesynchronization data pieces as representing erasure.

[0081] According to still another aspect of the invention, areproduction apparatus for reproducing a composite coded data piece froma recording medium having the composite coded data piece recordedthereon is provided. The composite coded data piece includes a firstcoded data piece which is error-correction-coded using a first errorcorrection code, a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,and a plurality of synchronization data pieces. The first coded datapiece includes a plurality of first symbols. The second coded data pieceincludes a plurality of second symbols. At least one first symbol isprovided between two adjacent synchronization data pieces among theplurality of synchronization data pieces. At least one of the pluralityof second symbols is provided at least between a synchronization datapiece and a first symbol. The reproduction apparatus includes a readingsection for reading the composite coded data piece from the recordingmedium and outputting the first coded data piece, the second coded datapiece, and the plurality of synchronization data pieces; asynchronization detection information generation section for detectingstates of the plurality of synchronization data pieces and generatingsynchronization detection information which represents the detectionresult; an error location information generation section for performingerror correction of the first coded data piece and generating errorlocation information which represents an error location of the firstcoded data; an erasure locator information generation section forgenerating erasure locator information which represents an erasureposition of the second coded data piece, based on the error locationinformation and the synchronization detection information; and anerasure error correction section for performing erasure error correctionof the second coded data piece based on the erasure locator information.When the synchronization detection information indicates that any two ormore data pieces from undetected synchronization data pieces andsynchronization data pieces detected with a positional offset areconsecutive, the erasure locator information generation sectiondetermines at least one second symbol provided between the consecutivesynchronization data pieces as representing erasure.

[0082] In one embodiment of the invention, the erasure locatorinformation generation section determines at least one first symbolprovided between the consecutive synchronization data pieces asrepresenting erasure.

[0083] According to still another aspect of the invention, areproduction apparatus for reproducing a composite coded data piece froma recording medium having the composite coded data piece recordedthereon is provided. The composite coded data piece includes a firstcoded data piece which is error-correction-coded using a first errorcorrection code, and a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code.The first coded data piece includes a plurality of first symbols. Thesecond coded data piece includes a plurality of second symbols. At leastone of the plurality of second symbols is provided between two adjacentfirst symbols of the plurality of first symbols. The reproductionapparatus includes a reading section for reading the composite codeddata piece from the recording medium and outputting the first coded datapiece and the second coded data piece; an error location informationgeneration section for performing error correction of the first codeddata piece and generating error location information which represents anerror location of the first coded data; an erasure locator informationgeneration section for generating at least first erasure locatorinformation and second erasure locator information which represent anerasure position of the second coded data piece, based on the errorlocation information; and an erasure error correction section forperforming erasure error correction of the second coded data piece basedon at least one of the first erasure locator information and the seconderasure locator information. When there is an error which cannot becorrected based on the first erasure locator information, the erasureerror correction section performs erasure error correction of the secondcoded data piece based on the second erasure locator information.

[0084] In one embodiment of the invention, when all the errors can becorrected based on the first erasure locator information, the erasurelocator information generation section generates erasure locatorinformation for erasure error correction of another second coded datapiece using an identical method as the method used for generating thefirst erasure locator information. When all the errors can be correctedbased on the second erasure locator information, the erasure locatorinformation generation section generates erasure locator information forerasure error correction of another second coded data piece using anidentical method as the method used for generating the second erasurelocator information.

[0085] In one embodiment of the invention, the plurality of firstsymbols include an Nth first symbol, an (N+1)th first symbol and an(N+2) the first symbol, where N is an integer. When the error locationinformation indicates that no error is detected in the Nth first symboland the (N+2)th first symbol and that an error is detected in the(N+1)th first symbol, the erasure locator information generation sectiondetermines at least one of the plurality of second symbols providedadjacent to the (N+1)th first symbol as representing erasure.

[0086] According to still another aspect of the invention, areproduction apparatus for reproducing a coded data piece from arecording medium having a plurality of synchronization data pieces andthe coded data piece which is error-correction-coded recorded thereon isprovided. The coded data piece includes a plurality of symbols. At leastone of the plurality of symbols is provided between two adjacentsynchronization data pieces among the plurality of synchronization datapieces. The reproduction apparatus includes a reading section forreading the plurality of synchronization data pieces and the coded datapiece from the recording medium; a synchronization detection informationgeneration section for detecting states of the plurality ofsynchronization data pieces and generating synchronization detectioninformation which represents the detection result; an erasure locatorinformation generation section for generating at least first erasurelocator information and second erasure locator information whichrepresent an erasure position of the coded data piece, based on thesynchronization detection information; and an erasure error correctionsection for performing erasure error correction of the coded data piecebased on at least one of the first erasure locator information and thesecond erasure locator information. When there is an error which cannotbe corrected based on the first erasure locator information, the erasureerror correction section performs erasure error correction of the codeddata piece based on the second erasure locator information.

[0087] In one embodiment of the invention, when all the errors can becorrected based on the first erasure locator information, the erasurelocator information generation section generates erasure locatorinformation for erasure error correction of another coded data pieceusing an identical method as the method used for generating the firsterasure locator information. When all the errors can be corrected basedon the second erasure locator information, the erasure locatorinformation generation section generates erasure locator information forerasure error correction of another coded data piece using an identicalmethod as the method used for generating the second erasure locatorinformation.

[0088] In one embodiment of the invention, the plurality ofsynchronization data pieces include an Nth synchronization data piece,an (N+1)th synchronization data piece, and an (N+2)th synchronizationdata piece, where N is an integer. When the synchronization detectioninformation indicates that the Nth synchronization data piece and the(N+2)th synchronization data piece are detected and the (N+1)thsynchronization data piece is not detected, the erasure locatorinformation generation section determines at least one of the pluralityof symbols provided adjacent to the (N+1)th synchronization data pieceas representing erasure.

[0089] In one embodiment of the invention, the plurality ofsynchronization data pieces include an Nth synchronization data pieceand an (N+1)th synchronization data piece, where N is an integer. Whenthe synchronization detection information indicates that the (N+1) thsynchronization data piece is detected with a positional offset, theerasure locator information generation section determines at least onesymbol provided between the Nth synchronization data piece and the(N+1)th synchronization data piece as representing erasure.

[0090] In one embodiment of the invention, when the synchronizationdetection information indicates that any two or more data pieces fromundetected synchronization data pieces and synchronization data piecesdetected with a positional offset are consecutive, the erasure locatorinformation generation section determines at least one symbol providedbetween the consecutive synchronization data pieces as representingerasure.

[0091] According to still another aspect of the invention, areproduction apparatus for reproducing a composite coded data piece froma recording medium having the composite coded data piece recordedthereon is provided. The composite coded data piece includes a firstcoded data piece which is error-correction-coded using a first errorcorrection code, a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,and a plurality of synchronization data pieces. The first coded datapiece includes a plurality of first symbols. The second coded data pieceincludes a plurality of second symbols. At least one first symbol isprovided between two adjacent synchronization data pieces among theplurality of synchronization data pieces. At least one of the pluralityof second symbols is provided at least between a synchronization datapiece and a first symbol. The reproduction apparatus includes a readingsection for reading the composite coded data piece from the recordingmedium and outputting the first coded data piece, the second coded datapiece, and the plurality of synchronization data pieces; asynchronization detection information generation section for detectingstates of the plurality of synchronization data pieces and generatingsynchronization detection information which represents the detectionresult; an error location information generation section for performingerror correction of the first coded data piece and generating errorlocation information which represents an error location of the firstcoded data; an erasure locator information generation section forgenerating at least first erasure locator information and second erasurelocator information which represent an erasure position of the secondcoded data piece, based on the error location information and thesynchronization detection information; and an erasure error correctionsection for performing erasure error correction of the second coded datapiece based on at least one of the first erasure locator information andthe second erasure locator information. When there is an error whichcannot be corrected based on the first erasure locator information, theerasure error correction section performs erasure error correction ofthe second coded data piece based on the second erasure locatorinformation.

[0092] In one embodiment of the invention, when all the errors can becorrected based on the first erasure locator information, the erasurelocator information generation section generates erasure locatorinformation for erasure error correction of another second coded datapiece using an identical method as the method used for generating thefirst erasure locator information. When all the errors can be correctedbased on the second erasure locator information, the erasure locatorinformation generation section generates erasure locator information forerasure error correction of another second coded data piece using anidentical method as the method used for generating the second erasurelocator information.

[0093] In one embodiment of the invention, when the synchronizationdetection information indicates that there is a synchronization datapiece which is not detected and the error location information indicatesthat no error is detected in the first symbols immediately on both sidesof the undetected synchronization data piece, the erasure locatorinformation generation section determines at least one of the pluralityof second symbols provided adjacent to the undetected synchronizationdata piece as representing erasure.

[0094] In one embodiment of the invention, at least two first symbolsare provided between two adjacent synchronization data pieces among theplurality of synchronization data pieces. At least one second symbol isprovided between two adjacent first symbols among the at least two firstsymbols. When the error location information indicates that there is afirst symbol detected to have an error and at least one of the errorlocation information and the synchronization detection informationindicates that one of a detected synchronization data piece and a firstsymbol detected to have no error is immediately on each of both sides ofthe first symbol detected to have an error, the erasure locatorinformation generation section determines at least one of the pluralityof second symbols provided adjacent to the first symbol detected to havean error as representing erasure.

[0095] In one embodiment of the invention, the plurality ofsynchronization data pieces include an Nth synchronization data pieceand an (N+1)th synchronization data piece, where N is an integer. Whenthe synchronization detection information indicates that the (N+1) thsynchronization data piece is detected with a positional offset, theerasure locator information generation section determines at least onesecond symbol provided between the Nth synchronization data piece andthe (N+1)th synchronization data piece as representing erasure.

[0096] In one embodiment of the invention, when the synchronizationdetection information indicates that any two or more data pieces fromundetected synchronization data pieces and synchronization data piecesdetected with a positional offset are consecutive, the erasure locatorinformation generation section determines at least one second symbolprovided between the consecutive synchronization data pieces asrepresenting erasure.

[0097] An error correction method and a reproduction apparatus accordingto the present invention function as follows. When a first symbolincluded in a first coded data piece having a relatively high degree ofredundancy is detected to have an error or when no synchronization datapiece is detected, the second symbols which are provided in the vicinityof such a first symbol or the undetected synchronization data piece havea high probability of incorrect and thus are determined to representerasure. When a synchronization data piece is detected with a positionaloffset, symbols included in the coded data pieces located before such asynchronization data piece have a high probability of being incorrectand thus is determined to represent erasure. Symbols included in thecoded data pieces located after such a synchronization data piece have ahigh probability of being correct and thus is determined not torepresent erasure. When at least two of the undetected synchronizationdata pieces and synchronization data pieces detected with a positionaloffset are consecutive, data pieces which are read before the nextcorrectly detected synchronization data piece have a high probability ofbeing incorrect. Thus, symbols included in all the coded data piecesbetween those consecutive synchronization data pieces are determined torepresent erasure. Owing to these methods, erasure positions can bedetermined with higher precision, and thus the error correctioncapability can be improved.

[0098] An error correction method and a reproduction apparatus accordingto the present invention are useful for, for example, error correctionof composite coded data.

[0099] Thus, the invention described herein makes possible theadvantages of providing an error correction method which is effectivefor generating erasure locator information using a result of errorcorrection of a first coded data piece or a result of detection of asynchronization data piece and for performing erasure error correctionof a second coded data piece using the erasure locator information, anda reproduction apparatus for carrying out such an error correctionmethod.

[0100] These and other advantages of the present invention will becomeapparent to those skilled in the art upon reading and understanding thefollowing detailed description with reference to the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0101]FIG. 1 is a flowchart illustrating an error correction method of acomposite coded data piece according to a first example of the presentinvention;

[0102]FIG. 2 shows a structure of a composite coded data piece;

[0103]FIG. 3 is a flowchart illustrating an error correction method of acomposite coded data piece;

[0104]FIG. 4 shows a state of a synchronization data piece or a firstsymbol when a second coded data piece is determined to represent erasurein the error correction method;

[0105]FIG. 5 shows another state of the synchronization data piece orthe first symbol when the second coded data piece is determined torepresent erasure in the error correction method;

[0106]FIG. 6 shows still another state of the synchronization data pieceor the first symbol when the second coded data piece is determined torepresent erasure in the error correction method;

[0107]FIG. 7 shows an exemplary pattern of errors of the composite codeddata piece;

[0108]FIG. 8 is a flowchart of a method for correcting an error of thefirst coded data piece and generating error location informationaccording to the first example of the present invention;

[0109]FIG. 9 shows a state of a synchronization data piece of a firstsymbol in the first example;

[0110]FIG. 10 shows another state of the synchronization data piece ofthe first symbol in the first example;

[0111]FIG. 11 shows still another state of the synchronization datapiece of the first symbol in the first example;

[0112]FIG. 12 is a flowchart of a method for correcting an erasure errorof a second coded data piece according to the first example;

[0113]FIG. 13 is a flowchart illustrating an error correction method ofa composite coded data piece according to a second example of thepresent invention; and

[0114]FIG. 14 shows an exemplary structure of an informationreproduction apparatus according to a third example of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0115] Hereinafter, the present invention will be described by way ofillustrative examples with reference to the accompanying drawings.

EXAMPLE 1

[0116] An error correction method according to a first example of thepresent invention will be described. In the following description, thecomposite coded data piece 203 shown in FIG. 2 will be used as anexample of the composite coded data piece.

[0117]FIG. 1 is a flowchart 10 illustrating an error correction methodof the composite coded data piece 203 in this example.

[0118] In step 101, the states of the synchronization data pieces 204and 205 are detected in the order of data pieces which have beenrecorded. Thus, synchronization detection information representing thedetection result is generated. When, for example, a synchronization datapiece is detected, the synchronization detection information associatedwith that synchronization data piece indicates “0”. When nosynchronization data piece is detected, the synchronization detectioninformation associated with that synchronization data piece indicates“1”. When a synchronization data piece is detected with a positionaloffset, the synchronization detection information associated with thatsynchronization data piece indicates “2”.

[0119] In step 102, the first coded data piece 201 is error-corrected.In step 103, error location information representing the position of anerror of the first coded data piece 201 is generated. Since the firstcoded data piece 201 is positioned after being interleaved, the errorcorrection is performed on a first coded data piece 201 which has beende-interleaved. As described above, de-interleaving is the oppositetransform to interleaving. In this manner, the first coded data pieces206 through 211 are error-corrected. This will be described in detailbelow.

[0120] In step 104, erasure locator information representing theposition of erasure of the second coded data piece 202 is generatedusing the synchronization detection information and the error locationinformation generated in steps 101 and 103. This will be described indetail below.

[0121] In step 105, the second coded data piece 202 iserasure-error-corrected using the erasure locator information generatedin step 104.

[0122]FIG. 8 is a flowchart 80 illustrating an exemplary method forcorrecting the error of the first coded data piece 201 and generatingerror location information as performed in steps 102 and 103 in FIG. 1.

[0123] In step 801, a syndrome representing position information forspecifying a position of an error is calculated. A data piece R to beerror-corrected is:

R=(A[0] A[1] . . . A[60] A[61])  expression 3

[0124] In this expression, A[i] (i=0 through 61)represents 1 byte, whichcorresponds to 8 bits. Here, the data size of one symbol is 1 byte. A[0]through A[29] represent a data portion, and A[30] through A[61]represent a parity portion. Syndrome S_(j) is defined as:

S _(j) =R(α³)=A[0]α^(61j) +A[1]α^(60j) + . . . +A[60]α^(j)+A[61]  expression 4

[0125] Here, j=0 through 31.

[0126] In step 802, it is determined whether syndrome S_(j) is 0 or not.When syndrome S_(j) is 0, the processing advances to step 810. In step810, it is determined that all the symbols A[i] (i=0 through 61)included in the data piece R are correct. In step 813, error locationinformation representing “0” regarding all the symbols A[i] (i=0 through61) is generated. When syndrome S_(j) is not 0 in step 802, theprocessing advances to step 803.

[0127] In step 803, an error locator polynomial is formulated usingsyndrome S_(j). The error locator polynomial has, as a root, thereciprocal number of error locations L1, L2, . . . Lm (m is the numberof errors) and is expressed by: $\begin{matrix}\begin{matrix}\begin{matrix}{{\alpha (x)} = {\left( {1 - {\alpha^{L1}x}} \right)\left( {1 - {\alpha^{L2}x}} \right)\quad \ldots \quad \left( {1 - \alpha^{Lm}} \right)}} \\{= {{\sigma_{m}x^{m}} + {\sigma_{m - 1}x^{m - 1}} + \ldots \quad + {\sigma_{1}x} + 1}}\end{matrix} & \quad\end{matrix} & {{expression}\quad 5}\end{matrix}$

[0128] Each coefficient of the error locator polynomial is defined bysyndrome S_(j). The coefficient of the error locator polynomial is foundusing Peterson's method, the Euclidean method, or an algorithm such asthe BM method. Peterson's method solves the simultaneous equationsrealized between the coefficient of the error locator polynomial andsyndrome S_(j), using a matrix. The Euclidean method is a sequentialcalculation method of solving such simultaneous equations using apolynomial.

[0129] When the coefficient of the error locator polynomial is found instep 804, the processing advances to step 805. When the coefficient isnot found, the processing advances to step 809. In step 809, it isdetermined that a larger number of errors than can be corrected aregenerated. In step 812, error location information representing “1”regarding all the symbols A[i] (i=0 through 61) is generated.

[0130] In step 805, α to the −ith power (i=0 through 61, and α is theroot of the primitive polynomial (expression 1)) is substituted into theerror locator polynomial. Thus, the value of “k”, at which the solutionof the error locator polynomial is 0, is found. In this way, theposition of the incorrect data piece (i.e., the error location) isfound. The symbol corresponding to the error location is represented as:

A[61−k]  expression 6.

[0131] In step 806, it is determined whether or not a calculation forfinding the error location can be performed. When it is determined thatthe calculation can be performed in step 806, the processing advances tostep 807. When it is determined that the calculation cannot be performedin step 806, error location information representing “1” regarding allthe symbols A[i] (i=0 through 61) is generated.

[0132] In step 807, an error value is calculated by solving thesimultaneous equations between the error location found in steps 805 and806 and syndrome S_(j).

[0133] In step 808, symbol A[61−k] is error-corrected by subtracting theerror value obtained in step 807 from the value represented by symbolA[61−k] corresponding to the error location found in steps 805 and 806.In step 811, error location information representing “1” regardingsymbol A[61−k] is generated. By performing such error correction andgeneration of error location information, the first coded data piece 201is error-corrected.

[0134] Hereinafter, a method for generating erasure locator informationin step 104 in FIG. 1 will be described in detail. Extinction positioninformation is generated by reading and using synchronization detectioninformation of synchronization data pieces positioned before and afterthe second coded data piece for which erasure locator information is tobe generated, and/or error location information of first coded datapieces positioned before and after the second coded data piece for whicherasure locator information is to be generated. In this example, amethod for generating erasure locator information in the case where thesynchronization data pieces and the first symbols are in the state shownin FIGS. 9 through 11. FIGS. 9 through 11 show a portion of the datacorresponding to one row (or a plurality of rows), in a recordingdirection, of the composite corrected data piece 203 which is arrangedin rows and columns.

[0135] In FIG. 9, mark “X” indicates a synchronization data piece, thesynchronization detection information of which represents “1”, or afirst symbol, the error location information of which represents “1”.Mark “◯” indicates a synchronization data piece, the synchronizationdetection information of which represents “0”, or a first symbol, theerror location information of which represents “0”.

[0136] In one embodiment, an Nth first symbol 901, an (N+1)th firstsymbol 902, and an (N+2)th first symbol 903 are arranged in a recordingdirection 908. Here, “N” is an integer. It is assumed that no error isdetected in the Nth first symbol 901 and the (N+2)th first symbol 903but an error is detected in the (N+1)th first symbol 902. In this case,at least one of a plurality of second symbols provided immediately onboth sides of the (N+1)th first symbol 902 is determined to representerasure. Thus, erasure locator information representing such adetermination result is generated.

[0137] As shown in FIG. 9, a second coded data piece 909 is arrangedbetween the Nth first symbol 901 and the (N+1)th first symbol 902. Thesecond coded data piece 909 is divided into two portions, i.e., partialsecond coded data pieces 904 and 906 in accordance with the number ofsecond symbols which are determined to represent erasure. The partialsecond coded data pieces 904 and 906 each include at least one secondsymbol. For generating erasure locator information, at least one secondsymbol included in the partial second coded data piece 904 providedadjacent to the (N+1)th first symbol 902 is determined to representerasure. At least one second symbol included in the partial second codeddata piece 906 provided adjacent to the Nth first symbol 901 isdetermined not to represent erasure.

[0138] A second coded data piece 910 is arranged between the (N+1)thfirst symbol 902 and the (N+2)th first symbol 903. The second coded datapiece 910 is divided into two portions, i.e., partial second coded datapieces 905 and 907 in accordance with the number of second symbols whichare determined to represent erasure. The partial second coded datapieces 905 and 907 each include at least one second symbol. Forgenerating erasure locator information, at least one second symbolincluded in the partial second coded data piece 905 provided adjacent tothe (N+1)th first symbol 902 is determined to represent erasure. Atleast one second symbol included in the partial second coded data piece907 provided adjacent to the (N+2)th first symbol 903 is determined notto represent erasure.

[0139] The number of second symbols which are determined to representerasure is arbitrary. For example, half of the plurality of secondsymbols included in each of the second coded data pieces 909 and 910which are held between the synchronization data pieces and/or the firstcoded data pieces may be determined to represent erasure. Alternatively,all such a plurality of second symbols may be determined to representerasure.

[0140] A second symbol determined to represent erasure is associatedwith erasure locator information representing “1”. A second symboldetermined not to represent erasure is associated with erasure locatorinformation representing “0”.

[0141] In another embodiment, the data pieces 901, 902 and 903 may besynchronization data pieces. In this case also, at least one of theplurality of second symbols arranged immediately on both sides of the(N+1)th synchronization data piece 902 is determined to representerasure. Thus, erasure locator information representing such adetermination result is generated.

[0142] For example, at least one second symbol included in the partialsecond coded data piece 904 adjacent to the (N+1)th synchronization datapiece 902 is determined to represent erasure. At least one second symbolincluded in the partial second coded data piece 906 adjacent to the Nthsynchronization data piece 901 is determined not to represent erasure.

[0143] In addition, for example, at least one second symbol included inthe partial second coded data piece 905 adjacent to the (N+1)thsynchronization data piece 902 is determined to represent erasure. Atleast one second symbol included in the partial second coded data piece907 adjacent to the (N+2)th synchronization data piece 903 is determinednot to represent erasure. In this case also, the number of secondsymbols determined to represent erasure is arbitrary.

[0144] In still another embodiment, at least one of the data pieces 901,902 and 903 (for example, the data piece 901) may be a synchronizationdata piece. The other data pieces are first symbols. In this case also,the erasure locator information is generated in the same procedure asthat described above. (The detailed description of the procedure willnot be repeated.)

[0145] The above-described method can be applied as follows to the casewhere the errors as shown in FIG. 7 occur. The second symbols located inerror location areas 710 and 711 are determined to represent erasure. Asa result of this determination, the partial second coded data pieces 704through 709 each include 12 second symbols determined to representerasure and 5 second symbols determined to represent an error. The totalnumber of the symbols determined to represent erasure and the totalnumber of the symbols determined to represent an error are each in therange of expression 2. Thus, error correction is possible.

[0146] In the case where error location information (or synchronizationdetection information) indicates that an error is detected in both ofthe two first symbols adjacent to each other (or two synchronizationdata pieces adjacent to each other), all the second symbols arrangedbetween the two first symbols (or the two synchronization data pieces)are determined to represent erasure.

[0147] Next, another method for generating erasure locator informationwill be described with reference to FIG. 10.

[0148] In FIG. 10, mark “X” indicates a synchronization data piece, thesynchronization detection information of which represents “1”, or afirst symbol, the error location information of which represents 1”.Mark “Δ” indicates a synchronization data piece, the synchronizationdetection information of which represents “2” (i.e., a synchronizationdata piece detected with a positional offset).

[0149] In one embodiment, an Nth synchronization data piece 1002, an(N+1)th synchronization data piece 1001, and an (N+2)th synchronizationdata piece 1003 are arranged in a recording direction 1006. At least asecond coded data piece 1004 is provided between the Nth synchronizationdata piece 1002 and the (N+1)th synchronization data piece 1001. Atleast a second coded data piece 1005 is provided between the (N+1)thsynchronization data piece 1001 and the (N+2)th synchronization datapiece 1003. The second encoded data pieces 1004 and 1005 each include atleast one second symbol. When, as shown in FIG. 10, the (N+1)thsynchronization data piece 1001 is detected with a positional offset, atleast one second symbol provided between the Nth synchronization datapiece 1002 and the (N+1)th synchronization data piece 1001 is determinedto represent erasure. At least one second symbol provided between the(N+1)th synchronization data piece 1001 and the (N+2)th synchronizationdata piece 1003 is determined not to represent erasure. The reason isthat symbols located before the synchronization data piece detected witha positional offset are incorrect with a high probability, and symbolslocated after the synchronization data piece detected with a positionaloffset are correctly reproduced with a high probability.

[0150] In another embodiment, the data pieces 1002 and 1003 may be firstsymbols. The first symbol 1002 is provided between the Nthsynchronization data piece and the (N+1)th synchronization data piece1001, and the first symbol 1003 is provided between the (N+1)thsynchronization data piece 1001 and the (N+2)th synchronization datapiece. In this case also, at least one second symbol provided betweenthe first symbol 1002 and the (N+1)th synchronization data piece 1001 isdetermined to represent erasure. At least one second symbol providedbetween the (N+1)th synchronization data piece 1001 and the first symbol1003 is determined not to represent erasure.

[0151] The second symbol determined to represent erasure is associatedwith erasure locator information representing “1”. The second symboldetermined not to represent erasure is associated with erasure locatorinformation representing “0”.

[0152] Using this method for generating erasure locator information, asymbol located before a synchronization data piece and having a highprobability of being incorrect can be determined to represent erasure.Thus, the number of symbols which can be corrected, among incorrectsymbols, is increased. This improves the error correction capability.Also using this method, a symbol located after a synchronization datapiece and having a high probability of being correctly reproduced can bedetermined not to represent erasure. Thus, correct symbols are notdetermined to represent erasure. As a result, the number of unnecessaryerasure positions is reduced, and effective erasure error correction canbe performed. This further improves the error correction capability.

[0153] Still another method for generating erasure locator informationwill be described with reference to FIG. 11.

[0154] In FIG. 11, mark “X” indicates a synchronization data piece, thesynchronization detection information of which represents “1” and/or afirst symbol, the error location information of which represents 1”.Mark “◯” indicates a synchronization data piece, the synchronizationdetection information of which represents “0” and/or a first symbol, theerror location information of which represents 0”. Mark “Δ” indicates asynchronization data piece, the synchronization detection information ofwhich represents “2”.

[0155] When no synchronization data piece is detected, data pieces whichare read before the next time a synchronization data piece is correctlydetected have a high probability of being incorrect. Therefore, when anytwo or more data pieces from the undetected synchronization data piecesand the synchronization data pieces detected with a positional offsetare consecutive, at least one first symbol and at least one secondsymbol provided between the consecutive synchronization data pieces aredetermined to represent erasure.

[0156] In one embodiment, synchronization data pieces 1101 and 1102, thesynchronization detection information of which represent “1”, areconsecutive in a recording direction 1118. In this case, even when afirst symbol 1104, the error location information of which represents“0”, exists between the synchronization data pieces 1101 and 1102, it isregarded that information represented by the first symbol 1104accidentally matches a correct code word. Thus, the first symbol 1104 isdetermined to represent erasure. The second symbols included in each ofsecond coded data pieces 1110, 1111, 1112 and 1113 between thesynchronization data pieces 1101 and 1102 are determined to representerasure. The second symbols determined to represent erasure are eachassociated with erasure locator information representing “1”.

[0157] In addition in FIG. 11, the synchronization data pieces 1102, thesynchronization detection information of which represent “1”, and asynchronization data piece, the synchronization detection information ofwhich represent “2”, are consecutive in the recording direction 1118. Inthis case, even when a first symbol 1108, the error location informationof which represents “0”, exists between the synchronization data pieces1102 and 1103, it is regarded that information represented by the firstsymbol 1108 accidentally matches a correct code word. Thus, the firstsymbol 1108 is determined to represent erasure. The second symbolsincluded in each of the second coded data pieces 1114, 1115, 1116 and1117 between the synchronization data pieces 1102 and 1103 aredetermined to represent erasure. The second symbols determined torepresent erasure are each associated with erasure locator informationrepresenting “1”. The first symbols 1105, 1106, 1107 and 1109 are firstsymbols determined to be incorrect.

[0158] Using this method for generating erasure, a first symbol, whichis not determined to be incorrect by the conventional methods because itaccidentally represents information matching the correct code worddespite the fact that it is actually incorrect, can now be determined tobe incorrect. Thus, a second symbol can now be correctly determined asrepresenting erasure, while the conventional methods fail in thisbecause the incorrect first symbol is detected as being correct.Therefore, the number of symbols which can be corrected, among incorrectsymbols, is increased. This improves the error correction capability.Since the erasure error correction can be performed with highercertainty, the erasure error correction capability is improved.

[0159]FIG. 12 is a flowchart 120 illustrating an exemplary method forcorrecting the erasure error of the second coded data piece 202 asperformed in step 105 in FIG. 1.

[0160] In step 1201, a syndrome representing position information forspecifying a position of an error is calculated. A data piece R to beerasure-error-corrected is:

R=(B[0] B[1] . . . B[246] B[247])  expression 7

[0161] In this expression, B[i] (i=0 through 247) represents 1 byte,which corresponds to 8 bits. Here, the data size of one symbol is 1byte. B[0] through B[215] represent a data portion which show a content(for example, video) or the like, and B[216] through B[247] represent aparity portion. Syndrome S_(j) is defined as:

S _(j) =R(α^(j))=B[0]α^(247j) +B[1]α^(246j) + . . . +B[246]α^(j)+B[247]  expression 8

[0162] Here, j=0 through 31.

[0163] In step 1202, it is determined whether syndrome S_(j) is 0 ornot. When syndrome S_(j) is 0, the processing advances to step 1210. Instep 1210, it is determined that all the symbols B[i] (i=0 through 247)included in the data piece Rare correct, and the erasure errorcorrection is terminated. When syndrome S_(j) is not 0 in step 1202, theprocessing advances to step 1203.

[0164] In step 1203, an error locator polynomial is formulated usingsyndrome S_(j) and the erasure locator information. The error locatorpolynomial has, as a root, the reciprocal number of error locations L1,L2, . . . Lm (m is the number of errors+the number of erasures) and isrepresented by expression 5 above.

[0165] The coefficient of the error locator polynomial is defined bysyndrome S_(j) and the erasure locator information. The coefficient ofthe error locator polynomial is found using Peterson's method, theEuclidean method, or an algorithm such as the BM method. Peterson'smethod solves the simultaneous equations realized between thecoefficient of the error locator polynomial, syndrome S_(j), and theerasure locator information, using a matrix. The Euclidean method is asequential calculation method of solving such simultaneous equationsusing a polynomial.

[0166] When the coefficient of the error locator polynomial is found instep 1204, the processing advances to step 1205. When the coefficient isnot found, the processing advances to step 1209. In step 1209, it isdetermined that a larger number of errors than can be corrected aregenerated. Thus, it is determined that the correction is impossible andthe erasure error correction procedure is terminated.

[0167] In step 1205, α to the −ith power (i=0 through 247, and α whichis the root of the primitive polynomial (expression 1)) is substitutedinto the error locator polynomial. Thus, the value of “k”, at which thesolution of the error locator polynomial is 0, is found. In this way,the position of the incorrect data piece (i.e., the error location) isfound. The symbol corresponding to the error location is represented as:

B[247−k]  expression 9.

[0168] In step 1206, it is determined whether or not a calculation forfinding the error location can be performed. When it is determined thatthe calculation can be performed in step 1206, the processing advancesto step 1207. When it is determined that the calculation cannot beperformed in step 1206, it is determined that correction is impossibleand the erasure error correction procedure is terminated in step 1209.

[0169] In step 1207, an error value is calculated by solving thesimultaneous equations between the error location found in steps 1205and 1206, syndrome S_(j) and the erasure locator information.

[0170] In step 1208, symbol B[247−k] is erasure-error-corrected bysubtracting the error value obtained in step 1207 from the data valuecorresponding to the error location found in steps 1205 and 1206. Then,the erasure error correction is terminated.

[0171] As described above, in the first example, when an error isdetected in a first symbol included in a first coded data piece having ahigh degree of redundancy or when no synchronization data piece isdetected (FIG. 9), second symbols provided in the vicinity of such afirst symbol or the undetected synchronization data piece have a highprobability of being incorrect and thus are determined to representerasure. When a synchronization data piece is detected with a positionaloffset (FIG. 10), symbols included in a coded data piece provided beforethat synchronization data piece have a high probability of beingincorrect and thus are determined to represent erasure, and symbolsincluded in a coded data piece provided after that synchronization datapiece have a low probability of being incorrect and thus are determinednot to represent erasure. When undetected synchronization data piecesand/or synchronization data pieces detected with a positional offset areconsecutive (FIG. 11), the data pieces, which are read before the nextcorrectly detected synchronization data piece, have a high probabilityof being incorrect. Therefore, symbols included in all the coded datapieces between those consecutive synchronization data pieces aredetermined to represent erasure. Owing to these methods, erasurepositions can be determined with higher precision, and thus the errorcorrection capability can be improved.

EXAMPLE 2

[0172] An error correction method according to a second example of thepresent invention will be described. In the following description, thecomposite coded data piece 203 shown in FIG. 2 will be used as anexample of the composite coded data piece.

[0173]FIG. 13 is a flowchart 130 illustrating an error correction methodof the composite coded data piece 203 in this example. Identical stepspreviously discussed with respect to FIG. 1 bear identical referencenumerals and the detailed descriptions thereof will be omitted.

[0174] The flowchart 130 is different from the flowchart 10 in FIG. 1 inthat in flowchart 130, when the second coded data piece is noterror-corrected, erasure error correction is performed repeatedly usingerasure locator information which is generated by a different erasurelocator information generation method. In this example, erasure errorcorrection is performed repeatedly until all the errors are corrected ortermination conditions are fulfilled.

[0175] Hereinafter, erasure error correction will be described whichuses a first erasure locator information generation method, a seconderasure locator information generation method, and a third erasurelocator information generation method and is terminated when all thefirst, second and third erasure locator information generation methodsare used (termination conditions). These three erasure locatorinformation generation methods are, for example, described withreference to FIGS. 9, 10 and 11.

[0176] Steps 101, 102 and 103 are performed. Then, in step 1301, thefirst erasure locator information generation method is first selected.

[0177] In step 1302, the first erasure locator information generationmethod is carried out using the synchronization detection informationand the error location information generated in steps 101 and 103. Thus,first erasure locator information is generated.

[0178] In step 105, the second coded data piece iserasure-error-corrected using the first erasure locator informationgenerated in step 1302. The post-correction second coded data piece isreferred to as a “first corrected data piece”.

[0179] In step 1303, it is determined whether all the errors have beencorrected or not. When the second coded data piece includes anuncorrected error in step 1303, the processing advances to step 1304.When all the errors have been corrected in step 1303, the errorcorrection procedure is terminated.

[0180] In step 1304, it is determined that the termination conditionsare not fulfilled since only one erasure error location informationgeneration method has been used. The processing returns to step 1301,where the second erasure error location information generation method isselected. The second erasure error location information generationmethod is different from the first erasure error location informationgeneration method already used.

[0181] In step 1302, the second erasure locator information generationmethod is carried out using the synchronization detection informationand the error location information generated in steps 101 and 103. Thus,second erasure locator information is generated.

[0182] In step 105, the first corrected data piece iserasure-error-corrected using the second erasure locator informationgenerated in step 1302. The post-correction first corrected data pieceis referred to as a “second corrected data piece”.

[0183] In step 1303, it is determined whether all the errors have beencorrected or not. When the first corrected data piece includes anuncorrected error in step 1303, the processing advances to step 1304.When all the errors have been corrected in step 1303, the errorcorrection procedure is terminated.

[0184] In step 1304, it is determined that the termination conditionsare not fulfilled since only two erasure error location informationgeneration methods have been used. The processing returns to step 1301,where the third erasure error location information generation method isselected. The third erasure error location information generation methodis different from the first erasure error location informationgeneration method and the second erasure error location informationgeneration method already used.

[0185] In step 1302, the third erasure locator information generationmethod is carried out using the synchronization detection informationand the error location information generated in steps 101 and 103. Thus,third erasure locator information is generated.

[0186] In step 105, the second corrected data piece iserasure-error-corrected using the third erasure locator informationgenerated in step 1302. The post-correction second corrected data pieceis referred to as a “third corrected data piece”.

[0187] In step 1303, it is determined whether all the errors have beencorrected or not. When the second corrected data piece includes anuncorrected error in step 1303, the processing advances to step 1304.When all the errors have been corrected in step 1303, the errorcorrection procedure is terminated.

[0188] In step 1304, it is determined that the termination conditionsare fulfilled since three erasure error location information generationmethods have been used. Thus, the error correction procedure isterminated.

[0189] In the second example, three erasure error location informationgeneration methods are used. The number of erasure error locationinformation generation methods used is arbitrary as long as it is two ormore. Any erasure error location information generation method which cangenerate erasure error location information is usable.

[0190] In step 1301 of the second example, the erasure error locationinformation generation methods are selected in the order of first,second and third erasure error location information generation methods.When all the errors are not corrected in step 105, even an erasure errorlocation information generation method which has already been used canbe selected as long as it is not the one which was used immediatelypreviously. When all of the errors can be corrected using a certainerasure error location information generation method, the same erasureerror location information generation method can be selected as thefirst erasure error location information generation method used for adifferent second coded data piece. For example, when all the errors canbe corrected using the first erasure error location information, thefirst erasure error location information generation method can be usedfor erasure error correction of a different second coded data piece.When all the errors can be corrected using the second erasure errorlocation information, the second erasure error location informationgeneration method can be used for erasure error correction of adifferent second coded data piece.

[0191] In the second example, the second and third erasure errorcorrection is performed on the first corrected data piece and the secondcorrected data piece. Alternatively, the erasure error correction may beperformed on the uncorrected second coded data piece.

[0192] In the second example, the procedure is terminated when all threeof the erasure error location information generation methods are used.This may be modified in various ways. For example, any possiblecombination of the three erasure error location information generationmethods may be performed in any possible order, or the three erasureerror location information generation methods maybe repeated until nocorrection is made.

[0193] As described above, in the second example, when erasure errorcorrection is performed using erasure error location informationgenerated by one erasure error location information generation methodbut there is at least one error which cannot be corrected, erasure errorcorrection is performed in repetition using erasure error locationinformation generated by another erasure error location informationgeneration method. Thus, errors which cannot be corrected by performingerasure error correction once can be corrected. This improves the errorcorrection capability.

EXAMPLE 3

[0194]FIG. 14 shows a structure of an information reproduction apparatus140 according to a third example of the present invention. Theinformation reproduction apparatus 140 carries out the error correctionmethods described in the first and second examples. An exemplaryoperation of the information reproduction apparatus 140 for correctingthe composite coded data piece 203 will be described, mainly using theerror correction method shown in FIG. 13. FIGS. 1, 2, 8, 9, 10, 11 and12 will also be referred to, but detailed descriptions thereof will notbe repeated.

[0195] The information reproduction apparatus 140 includes areproduction control circuit 1402, a rewritable memory 1403, an errorcorrection circuit 1408, a microcomputer 1411, and a program memory1412. A recording medium 1401 has the composite coded data piece 203shown in FIG. 2 recorded thereon in the recording direction 202. Thecomposite coded data piece 203 is merely an example of data which can berecorded on the recording medium 1401.

[0196] The reproduction control circuit 1402 includes a reading section1402A for reading a composite coded data piece from the recording medium1401 and outputting a first coded data piece, a second coded data piece,and a plurality of synchronization data pieces; and a synchronizationdetection information generation section 1402B for detecting the statesof the plurality of synchronization data pieces and generatingsynchronization detection information representing the detection result.

[0197] The rewritable memory 1403 includes a reproduction data area1404, a synchronization detection information area 1405, an errorlocation information area 1406, and an erasure locator information area1407. The error correction circuit 1408 includes a first errorcorrection circuit 1409 and a second error correction circuit 1410. Thefirst error correction circuit 1409 acts as an error locationinformation generation section for error-correcting the first coded datapiece and generating error location information representing an errorlocation of the first coded data piece. The second error correctioncircuit 1410 acts as an erasure error correction section forerasure-error-correcting the second coded data piece based on theerasure locator information. The microcomputer 1411 acts as an erasurelocator information generation section for generating erasure locatorinformation representing an erasure position of the second coded datapiece based on the error location information and the synchronizationdetection information.

[0198] As the rewritable memory 1403, a static memory (e.g., SRAM) whichdoes not require a data storing operation or a dynamic memory (e.g.DRAM) which requires a data storing operation may be used. In the thirdexample, the area of the rewritable memory 1403 is divided into aplurality of areas which are used as different memory areas.Alternatively, the information reproduction apparatus 140 may include aplurality of rewritable memories 140 for respectively storing differenttypes of data.

[0199] The program memory 1412 includes an erasure locator informationgeneration program 1413 and a termination condition branching program1414.

[0200] The erasure locator information generation program 1413 causesthe microcomputer 1411 to carry out the erasure locator informationgeneration method described in steps 1301 and 1302 in FIG. 13. Themicrocomputer 1411 generates erasure locator information using thesynchronization detection information and the error location informationwhich are stored in the rewritable memory 1403, and stores the generatederasure locator information in the erasure locator information area1407.

[0201] The termination condition branching program 1414 causes themicrocomputer 1411 to carry out the termination condition determinationdescribed in steps 1303 and 1304 in FIG. 13. When it is determined thatthe termination conditions are fulfilled, the microcomputer 1411terminates the error correction procedure. When it is determined thatthe termination conditions are not fulfilled, the microcomputer 1411executes another erasure locator information generation method based onthe erasure locator information generation program 1413.

[0202] The reading section 1402A included in the reproduction controlcircuit 1402 reads the composite coded data piece 203 from the recordingmedium 1401. When the reproduced first and second coded data pieces havebeen interleaved, the reading section 1402A de-interleaves these datapieces. The reproduced first and second coded data pieces 201 and 202are stored in the reproduction data area 1404. The reproduction dataarea 1404 may be divided into an area for storing the first coded datapiece 201 and an area for storing the second coded data piece 202. Thesynchronization detection information generation section 1402B includedin the reproduction control circuit 1402 detects a plurality ofsynchronization data pieces including the synchronization data pieces204 and 205. The synchronization detection information generationsection 1402B then executes, for example, the synchronization detectioninformation generation method described in step 101 in FIG. 1 so as togenerate synchronization detection information 1402C. Thesynchronization detection information generation section 1402B storesthe generated synchronization detection information 1402C in thesynchronization detection information area 1405.

[0203] The first error correction circuit 1409 performs error correctionon the first coded data piece 201 which is stored in the reproductiondata area 1404. The first error correction circuit 1409 then executes,for example, the error location information generation method describedin steps 811 through 813 in FIG. 8 so as to generate error locationinformation 1409A. The first error correction circuit 1409 stores thegenerated error location information 1409A in the error locationinformation area 1406. Any circuit may be used as the first errorcorrection circuit 1409 as long as it can perform the processing shownin FIG. 8 on the first coded data piece 201 stored in the reproductiondata area 1404 and store the generated error location information 1409Ain the error location information area 1406.

[0204] The microcomputer 1411 analyzes and executes the erasure locatorinformation generation program 1413 stored in the program memory 1412 soas to generate erasure locator information 1411A, and stores thegenerated erasure locator information 1411A in the erasure locatorinformation area 1407. When being notified by the second errorcorrection circuit 1410 that the error is not correctable, themicrocomputer 1411 analyzes and executes the termination conditionbranching program 1414. When the termination conditions are determinedto be fulfilled, the microcomputer 1411 terminates the error correctionprocedure. When the termination conditions are determined not to befulfilled, the microcomputer 1411 analyzes and executes another erasurelocator information generation method contained in the erasure locatorinformation generation program 1413. Thus, the microcomputer 1411generates another erasure locator information 1411B used for repeatingerasure error correction and stores the erasure locator information1411B in the erasure locator information area 1407.

[0205] The second error correction circuit 1410 performs erasure errorcorrection of the second coded data piece 202 which is stored in thereproduction data area 1404 using the erasure locator information 1411Aor the erasure locator information 1411B stored in the erasure locatorinformation area 1407. The second error correction circuit 1410 notifiesthe error correction result to the microcomputer 1411. Any circuit maybe used as the second error correction circuit 1410 as long as it canperform the processing shown in FIG. 12 on the second coded data piece202 stored in the reproduction data area 1404 and notify themicrocomputer 1411 whether error correction has been performed (step1208 in FIG. 12), error correction is impossible (step 1209) or there isno error (step 1210).

[0206] In the third example, the information reproduction apparatus 140reproduces the first coded data piece 201 and the second coded datapiece 202 using an error correction method. The structures of the firstcoded data piece 201 and the second coded data piece 202 shown in FIG. 2are merely exemplary. Any codes may be used as the first errorcorrection code and the second error correction code as long as thefirst error correction code has a higher degree of redundancy than thatof the second error correction code.

[0207] A part of the procedure performed by the reproduction controlcircuit 1402 and the error correction circuit 1408 may be executed usingsoftware. The procedure performed by the erasure locator informationgeneration program 1413 and the termination condition branching program1414 may be executed by hardware instead of using the programs 1413 and1414.

[0208] If all the procedures performed by the information reproductionapparatus 140 are executed by hardware, one device of hardware isrequired for each of the plurality of erasure locator informationgeneration methods. This excessively enlarges the scale of theapparatus. If all the procedures performed by the informationreproduction apparatus 140 are executed by software, an excessively longtime is required. In the third example, the procedure of generatingerasure locator information is performed by software, and otherprocedures are performed by hardware. Thus, erasure error correction canbe performed in repetition merely by reading different programs from theprogram memory 1412. This can reduce the scale of the hardware andshortens the processing time. The information reproduction apparatus 140is superior in terms of the time required for designing and costs tosystems of either executing all the procedures by hardware or executingall the procedures by software.

[0209] An error correction method and a reproduction apparatus accordingto the present invention function as follows. When a first symbolincluded in a first coded data piece having a relatively high degree ofredundancy is detected to have an error or when no synchronization datapiece is detected, the second symbols which are provided in the vicinityof such a first symbol or the undetected synchronization data piece havea high probability of incorrect and thus are determined to representerasure. When a synchronization data piece is detected with a positionaloffset, symbols included in the coded data pieces located before such asynchronization data piece have a high probability of being incorrectand thus is determined to represent erasure. Symbols included in thecoded data pieces located after such a synchronization data piece have ahigh probability of being correct and thus is determined not torepresent erasure. When at least two of the undetected synchronizationdata pieces and synchronization data pieces detected with a positionaloffset are consecutive, data pieces which are read before the nextcorrectly detected synchronization data piece have a high probability ofbeing incorrect. Thus, symbols included in all the coded data piecesbetween those consecutive synchronization data pieces are determined torepresent erasure. Owing to these methods, erasure positions can bedetermined with higher precision, and thus the error correctioncapability can be improved.

[0210] An error correction method and a reproduction apparatus accordingto the present invention are useful for, for example, error correctionof composite coded data.

[0211] Various other modifications will be apparent to and can bereadily made by those skilled in the art without departing from thescope and spirit of this invention. Accordingly, it is not intended thatthe scope of the claims appended hereto be limited to the description asset forth herein, but rather that the claims be broadly construed.

What is claimed is:
 1. A reproduction method for reproducing a compositecoded data piece from a recording medium having the composite coded datapiece recorded thereon, wherein: the composite coded data piece includesa first coded data piece which is error-correction-coded using a firsterror correction code, and a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,the first coded data piece includes a plurality of first symbols, thesecond coded data piece includes a plurality of second symbols, at leastone of the plurality of second symbols is provided between two adjacentfirst symbols of the plurality of first symbols, and the plurality offirst symbols include an Nth first symbol, an (N+1)th first symbol andan (N+2)th first symbol, where N is an integer, the reproduction methodcomprising: a reading step of reading the composite coded data piecefrom the recording medium and outputting the first coded data piece andthe second coded data piece; an error location information generationstep of performing error correction of the first coded data piece andgenerating error location information which represents an error locationof the first coded data; an erasure locator information generation stepof generating erasure locator information which represents an erasureposition of the second coded data piece, based on the error locationinformation; and an erasure error correction step of performing erasureerror correction of the second coded data piece based on the erasurelocator information, wherein the erasure locator information generationstep includes the step of, when the error location information indicatesthat no error is detected in the Nth first symbol and the (N+2)th firstsymbol and that an error is detected in the (N+1)th first symbol,determining at least one of the plurality of second symbols providedadjacent to the (N+1)th first symbol as representing erasure.
 2. Areproduction method according to claim 1, wherein the erasure locatorinformation generation step further includes the step of, when the errorlocation information indicates that no error is detected in the Nthfirst symbol and the (N+2)th first symbol and that an error is detectedin the (N+1)th first symbol, determining at least one second symbolprovided adjacent to the (N+1) th first symbol, among at least onesecond symbol provided between the Nth first symbol and the (N+1)thfirst symbol as representing erasure; and determining at least onesecond symbol provided adjacent to the (N+1)th first symbol, among atleast one second symbol provided between the (N+1)th first symbol andthe (N+2)th first symbol as representing erasure.
 3. A reproductionmethod according to claim 1, wherein the erasure locator informationgeneration step further includes the step of, when the error locationinformation indicates that an error is detected in both of two adjacentfirst symbols, determining all the second symbols provided between thetwo adjacent first symbols as representing erasure.
 4. A reproductionmethod for reproducing a composite coded data piece from a recordingmedium having the composite coded data piece recorded thereon, wherein:the composite coded data piece includes a first coded data piece whichis error-correction-coded using a first error correction code, and asecond coded data piece which is error-correction-coded using a seconderror correction code having a lower degree of redundancy than that ofthe first error correction code, the first coded data piece includes aplurality of first symbols, the second coded data piece includes aplurality of second symbols, and at least two of the plurality of secondsymbols are provided between two adjacent first symbols of the pluralityof first symbols, the reproduction method comprising: a reading step ofreading the composite coded data piece from the recording medium andoutputting the first coded data piece and the second coded data piece;an error location information generation step of performing errorcorrection of the first coded data piece and generating error locationinformation which represents an error location of the first coded data;an erasure locator information generation step of generating erasurelocator information which represents an erasure position of the secondcoded data piece, based on the error location information; and anerasure error correction step of performing erasure error correction ofthe second coded data piece based on the erasure locator information,wherein the erasure locator information generation step includes thestep of, when the error location information indicates that a firstsymbol detected to have no error and a first symbol detected to have anerror are adjacent to each other, determining at least one second symbolprovided adjacent to the first symbol detected to have an error, amongat least two second symbols provided between the first symbol detectedto have no error and the first symbol detected to have an error, asrepresenting erasure; and determining at least one second symbolprovided adjacent to the first symbol detected to have no error as notrepresenting erasure.
 5. A reproduction method according to claim 4,wherein the erasure locator information generation step further includesthe step of, when the error location information indicates that an erroris detected in both of two adjacent first symbols, determining all thesecond symbols provided between the two adjacent first symbols asrepresenting erasure.
 6. A reproduction method for reproducing a codeddata piece from a recording medium having a plurality of synchronizationdata pieces and the coded data piece which is error-correction-codedrecorded thereon, wherein: the coded data piece includes a plurality ofsymbols, at least one of the plurality of symbols is provided betweentwo adjacent synchronization data pieces among the plurality ofsynchronization data pieces, and the plurality of synchronization datapieces include an Nth synchronization data piece, an (N+1)thsynchronization data piece, and an (N+2)th synchronization data piece,where N is an integer, the reproduction method comprising: a readingstep of reading the plurality of synchronization data pieces and thecoded data piece from the recording medium; a synchronization detectioninformation generation step of detecting states of the plurality ofsynchronization data pieces and generating synchronization detectioninformation which represents the detection result; an erasure locatorinformation generation step of generating erasure locator informationwhich represents an erasure position of the coded data piece, based onthe synchronization detection information; and an erasure errorcorrection step of performing erasure error correction of the coded datapiece based on the erasure locator information, wherein the erasurelocator information generation step includes the step of, when thesynchronization detection information indicates that the Nthsynchronization data piece and the (N+2)th synchronization data pieceare detected and the (N+1)th synchronization data piece is not detected,determining at least one of the plurality of symbols provided adjacentto the (N+1)th synchronization data piece as representing erasure.
 7. Areproduction method according to claim 6, wherein the erasure locatorinformation generation step further includes the step of, when thesynchronization detection information indicates that the Nthsynchronization data piece and the (N+2)th synchronization data pieceare detected and the (N+1)th synchronization data piece is not detected,determining at least one symbol provided adjacent to the (N+1)thsynchronization data piece, among at least one symbol provided betweenthe Nth synchronization data piece and the (N+1)th synchronization datapiece as representing erasure; and determining at least one symbolprovided adjacent to the (N+1)th synchronization data piece, among atleast one symbol provided between the (N+1)th synchronization data pieceand the (N+2)th synchronization data piece as representing erasure.
 8. Areproduction method according to claim 6, wherein the erasure locatorinformation generation step further includes the step of, when thesynchronization detection information indicates that neither of the twoadjacent synchronization data pieces are detected, determining all thesymbols provided between the two undetected synchronization data piecesas representing erasure.
 9. A reproduction method for reproducing acoded data piece from a recording medium having a plurality ofsynchronization data pieces and the coded data piece which iserror-correction-coded recorded thereon, wherein: the coded data pieceincludes a plurality of symbols, and at least two of the plurality ofsymbols are provided between two adjacent synchronization data pieces ofthe plurality of synchronization data pieces, the reproduction methodcomprising: a reading step of reading the plurality of synchronizationdata pieces and the coded data piece from the recording medium; asynchronization detection information generation step of detectingstates of the plurality of synchronization data pieces and generatingsynchronization detection information which represents the detectionresult; an erasure locator information generation step of generatingerasure locator information which represents an erasure position of thecoded data piece, based on the synchronization detection information;and an erasure error correction step of performing erasure errorcorrection of the coded data piece based on the erasure locatorinformation, wherein the erasure locator information generation stepincludes the step of, when the synchronization detection informationindicates that a synchronization data piece adjacent to a detectedsynchronization data piece is not detected, determining at least onesymbol adjacent to the undetected synchronization data piece, among atleast two symbols provided between the detected synchronization datapiece and the undetected synchronization data piece, as representingerasure; and determining at least one symbol provided adjacent to thedetected synchronization data piece as not representing erasure.
 10. Areproduction method according to claim 9, wherein the erasure locatorinformation generation step further includes the step of, when thesynchronization detection information indicates that neither of the twoadjacent synchronization data pieces are detected, determining all thesymbols provided between the two undetected synchronization data piecesas representing erasure.
 11. A reproduction method for reproducing acomposite coded data piece from a recording medium having the compositecoded data piece recorded thereon, wherein: the composite coded datapiece includes a first coded data piece which is error-correction-codedusing a first error correction code, a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,and a plurality of synchronization data pieces, the first coded datapiece includes a plurality of first symbols, the second coded data pieceincludes a plurality of second symbols, at least one first symbol isprovided between two adjacent synchronization data pieces among theplurality of synchronization data pieces, and at least one of theplurality of second symbols is provided at least between asynchronization data piece and a first symbol, the reproduction methodcomprising: a reading step of reading the composite coded data piecefrom the recording medium and outputting the first coded data piece, thesecond coded data piece, and the plurality of synchronization datapieces; a synchronization detection information generation step ofdetecting states of the plurality of synchronization data pieces andgenerating synchronization detection information which represents thedetection result; an error location information generation step ofperforming error correction of the first coded data piece and generatingerror location information which represents an error location of thefirst coded data; an erasure locator information generation step ofgenerating erasure locator information which represents an erasureposition of the second coded data piece, based on the error locationinformation and the synchronization detection information; and anerasure error correction step of performing erasure error correction ofthe second coded data piece based on the erasure locator information,wherein the erasure locator information generation step includes thestep of, when the synchronization detection information indicates thatthere is a synchronization data piece which is not detected and theerror location information indicates that no error is detected in thefirst symbols immediately on both sides of the undetectedsynchronization data piece, determining at least one of the plurality ofsecond symbols provided adjacent to the undetected synchronization datapiece as representing erasure.
 12. A reproduction method according toclaim 11, wherein: at least two first symbols are provided between twoadjacent synchronization data pieces among the plurality ofsynchronization data pieces, at least one second symbol is providedbetween two adjacent first symbols among the at least two first symbols,and the erasure locator information generation step further includes thestep of, when the error location information indicates that there is afirst symbol detected to have an error and at least one of the errorlocation information and the synchronization detection informationindicates that one of a detected synchronization data piece and a firstsymbol detected to have no error is immediately on each of both sides ofthe first symbol detected to have an error, determining at least one ofthe plurality of second symbols provided adjacent to the first symboldetected to have an error as representing erasure.
 13. A reproductionmethod for reproducing a coded data piece from a recording medium havinga plurality of synchronization data pieces and the coded data piecewhich is error-correction-coded recorded thereon, wherein: the codeddata piece includes a plurality of symbols, at least one of theplurality of symbols is provided between two adjacent synchronizationdata pieces among the plurality of synchronization data pieces, and theplurality of synchronization data pieces include an Nth synchronizationdata piece and an (N+1)th synchronization data piece, where N is aninteger, the reproduction method comprising: a reading step of readingthe plurality of synchronization data pieces and the coded data piecefrom the recording medium; a synchronization detection informationgeneration step of detecting states of the plurality of synchronizationdata pieces and generating synchronization detection information whichrepresents the detection result; an erasure locator informationgeneration step of generating erasure locator information whichrepresents an erasure position of the coded data piece, based on thesynchronization detection information; and an erasure error correctionstep of performing erasure error correction of the coded data piecebased on the erasure locator information, wherein the erasure locatorinformation generation step includes the step of, when thesynchronization detection information indicates that the (N+1)thsynchronization data piece is detected with a positional offset,determining at least one symbol provided between the Nth synchronizationdata piece and the (N+1)th synchronization data piece as representingerasure.
 14. A reproduction method according to claim 13, wherein: theplurality of synchronization data pieces include an (N+2)thsynchronization data piece, and the erasure locator informationgeneration step further includes the step of, when the synchronizationdetection information indicates that the (N+1)th synchronization datapiece is detected with a positional offset, determining at least onesymbol provided between the (N+1)th synchronization data piece and the(N+2)th synchronization data piece as not representing erasure.
 15. Areproduction method for reproducing a composite coded data piece from arecording medium having the composite coded data piece recorded thereon,wherein: the composite coded data piece includes a first coded datapiece which is error-correction-coded using a first error correctioncode, a second coded data piece which is error-correction-coded using asecond error correction code having a lower degree of redundancy thanthat of the first error correction code, and a plurality ofsynchronization data pieces, the first coded data piece includes aplurality of first symbols, the second coded data piece includes aplurality of second symbols, at least one first symbol is providedbetween two adjacent synchronization data pieces among the plurality ofsynchronization data pieces, at least one of the plurality of secondsymbols is provided at least between a synchronization data piece and afirst symbol, and the plurality of synchronization data pieces includean Nth synchronization data piece and an (N+1)th synchronization datapiece, where N is an integer, the reproduction method comprising: areading step of reading the composite coded data piece from therecording medium and outputting the first coded data piece, the secondcoded data piece, and the plurality of synchronization data pieces; asynchronization detection information generation step of detectingstates of the plurality of synchronization data pieces and generatingsynchronization detection information which represents the detectionresult; an error location information generation step of performingerror correction of the first coded data piece and generating errorlocation information which represents an error location of the firstcoded data; an erasure locator information generation step of generatingerasure locator information which represents an erasure position of thesecond coded data piece, based on the error location information and thesynchronization detection information; and an erasure error correctionstep of performing erasure error correction of the second coded datapiece based on the erasure locator information, wherein the erasurelocator information generation step includes the step of, when thesynchronization detection information indicates that the (N+1)thsynchronization data piece is detected with a positional offset,determining at least one second symbol provided between the Nthsynchronization data piece and the (N+1)th synchronization data piece asrepresenting erasure.
 16. A reproduction method according to claim 15,wherein: the plurality of synchronization data pieces include an (N+2)thsynchronization data piece, and the erasure locator informationgeneration step further includes the step of, when the synchronizationdetection information indicates that the (N+1)th synchronization datapiece is detected with a positional offset, determining at least onesecond symbol provided between the (N+1)th synchronization data pieceand the (N+2)th synchronization data piece as not representing erasure.17. A reproduction method for reproducing a composite coded data piecefrom a recording medium having the composite coded data piece recordedthereon, wherein: the composite coded data piece includes a first codeddata piece which is error-correction-coded using a first errorcorrection code, a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,and a plurality of synchronization data pieces, the first coded datapiece includes a plurality of first symbols, the second coded data pieceincludes a plurality of second symbols, at least one first symbol isprovided between two adjacent synchronization data pieces among theplurality of synchronization data pieces, at least one of the pluralityof second symbols is provided at least between a synchronization datapiece and a first symbol, the plurality of synchronization data piecesinclude an Nth synchronization data piece and an (N+1)th synchronizationdata piece, where N is an integer, and a prescribed first symbol isprovided between the Nth synchronization data piece and the (N+1)thsynchronization data piece, the reproduction method comprising: areading step of reading the composite coded data piece from therecording medium and outputting the first coded data piece, the secondcoded data piece, and the plurality of synchronization data pieces; asynchronization detection information generation step of detectingstates of the plurality of synchronization data pieces and generatingsynchronization detection information which represents the detectionresult; an error location information generation step of performingerror correction of the first coded data piece and generating errorlocation information which represents an error location of the firstcoded data; an erasure locator information generation step of generatingerasure locator information which represents an erasure-position of thesecond coded data piece, based on the error location information and thesynchronization detection information; and an erasure error correctionstep of performing erasure error correction of the second coded datapiece based on the erasure locator information, wherein the erasurelocator information generation step includes the step of, when thesynchronization detection information indicates that the (N+1) thsynchronization data piece is detected with a positional offset,determining at least one second symbol provided between the prescribedfirst symbol and the (N+1)th synchronization data piece as representingerasure.
 18. A reproduction method according to claim 17, wherein: theplurality of synchronization data pieces include an (N+2)thsynchronization data piece, another prescribed first symbol is providedbetween the (N+1)th synchronization data piece and the (N+2)thsynchronization data piece, and the erasure locator informationgeneration step further includes the step of, when the synchronizationdetection information indicates that the (N+1)th synchronization datapiece is detected with a positional offset, determining at least onesecond symbol provided between the (N+1)th synchronization data pieceand the another prescribed first symbol as not representing erasure. 19.A reproduction method for reproducing a coded data piece from arecording medium having a plurality of synchronization data pieces andthe coded data piece which is error-correction-coded recorded thereon,wherein: the coded data piece includes a plurality of symbols, and atleast one of the plurality of symbols is provided between two adjacentsynchronization data pieces of the plurality of synchronization datapieces, the reproduction method comprising: a reading step of readingthe plurality of synchronization data pieces and the coded data piecefrom the recording medium; a synchronization detection informationgeneration step of detecting states of the plurality of synchronizationdata pieces and generating synchronization detection information whichrepresents the detection result; an erasure locator informationgeneration step of generating erasure locator information whichrepresents an erasure position of the coded data piece, based on thesynchronization detection information; and an erasure error correctionstep of performing erasure error correction of the coded data piecebased on the erasure locator information, wherein the erasure locatorinformation generation step includes the step of, when thesynchronization detection information indicates that any two or moredata pieces from undetected synchronization data pieces andsynchronization data pieces detected with a positional offset areconsecutive, determining at least one symbol provided between theconsecutive synchronization data pieces as representing erasure.
 20. Areproduction method for reproducing a composite coded data piece from arecording medium having the composite coded data piece recorded thereon,wherein: the composite coded data piece includes a first coded datapiece which is error-correction-coded using a first error correctioncode, a second coded data piece which is error-correction-coded using asecond error correction code having a lower degree of redundancy thanthat of the first error correction code, and a plurality ofsynchronization data pieces, the first coded data piece includes aplurality of first symbols, the second coded data piece includes aplurality of second symbols, at least one first symbol is providedbetween two adjacent synchronization data pieces among the plurality ofsynchronization data pieces, and at least one of the plurality of secondsymbols is provided at least between a synchronization data piece and afirst symbol, the reproduction method comprising: a reading step ofreading the composite coded data piece from the recording medium andoutputting the first coded data piece, the second coded data piece, andthe plurality of synchronization data pieces; a synchronizationdetection information generation step of detecting states of theplurality of synchronization data pieces and generating synchronizationdetection information which represents the detection result; an errorlocation information generation step of performing error correction ofthe first coded data piece and generating error location informationwhich represents an error location of the first coded data; an erasurelocator information generation step of generating erasure locatorinformation which represents an erasure position of the second codeddata piece, based on the error location information and thesynchronization detection information; and an erasure error correctionstep of performing erasure error correction of the second coded datapiece based on the erasure locator information, wherein the erasurelocator information generation step of, when the synchronizationdetection information indicates that any two or more data pieces fromundetected synchronization data pieces and synchronization data piecesdetected with a positional offset are consecutive, determining at leastone second symbol provided between the consecutive synchronization datapieces as representing erasure.
 21. A reproduction method according toclaim 20, wherein the erasure locator information generation stepfurther includes the step of determining at least one first symbolprovided between the consecutive synchronization data pieces asrepresenting erasure.
 22. A reproduction method for reproducing acomposite coded data piece from a recording medium having the compositecoded data piece recorded thereon, wherein: the composite coded datapiece includes a first coded data piece which is error-correction-codedusing a first error correction code, and a second coded data piece whichis error-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,the first coded data piece includes a plurality of first symbols, thesecond coded data piece includes a plurality of second symbols, and atleast one of the plurality of second symbols is provided between twoadjacent first symbols of the plurality of first symbols, thereproduction method comprising: a reading step of reading the compositecoded data piece from the recording medium and outputting the firstcoded data piece and the second coded data piece; an error locationinformation generation step of performing error correction of the firstcoded data piece and generating error location information whichrepresents an error location of the first coded data; an erasure locatorinformation generation step of generating at least first erasure locatorinformation and second erasure locator information which represent anerasure position of the second coded data piece, based on the errorlocation information; and an erasure error correction step of performingerasure error correction of the second coded data piece based on atleast one of the first erasure locator information and the seconderasure locator information, wherein the erasure error correction stepincludes the step of, when there is an error which cannot be correctedbased on the first erasure locator information, performing erasure errorcorrection of the second coded data piece based on the second erasurelocator information.
 23. A reproduction method according to claim 22,wherein: the erasure locator information generation step includes thesteps of: when all the errors can be corrected based on the firsterasure locator information, generating erasure locator information forerasure error correction of another second coded data piece using anidentical method as the method used for generating the first erasurelocator information, and when all the errors can be corrected based onthe second erasure locator information, generating erasure locatorinformation for erasure error correction of another second coded datapiece using an identical method as the method used for generating thesecond erasure locator information.
 24. A reproduction method accordingto claim 22, wherein: the plurality of first symbols include an Nthfirst symbol, an (N+1)th first symbol and an (N+2)th first symbol, whereN is an integer, and the erasure locator information generation stepincludes the step of, when the error location information indicates thatno error is detected in the Nth first symbol and the (N+2)th firstsymbol and that an error is detected in the (N+1)th first symbol,determining at least one of the plurality of second symbols providedadjacent to the (N+1)th first symbol as representing erasure.
 25. Areproduction method for reproducing a coded data piece from a recordingmedium having a plurality of synchronization data pieces and the codeddata piece which is error-correction-coded recorded thereon, wherein:the coded data piece includes a plurality of symbols, and at least oneof the plurality of symbols is provided between two adjacentsynchronization data pieces among the plurality of synchronization datapieces, the reproduction method comprising: a reading step of readingthe plurality of synchronization data pieces and the coded data piecefrom the recording medium; a synchronization detection informationgeneration step of detecting states of the plurality of synchronizationdata pieces and generating synchronization detection information whichrepresents the detection result; an erasure locator informationgeneration step of generating at least first erasure locator informationand second erasure locator information which represent an erasureposition of the coded data piece, based on the synchronization detectioninformation; and an erasure error correction step of performing erasureerror correction of the coded data piece based on at least one of thefirst erasure locator information and the second erasure locatorinformation, wherein the erasure error correction step includes the stepof, when there is an error which cannot be corrected based on the firsterasure locator information, performing erasure error correction of thecoded data piece based on the second erasure locator information.
 26. Areproduction method according to claim 25, wherein: the erasure locatorinformation generation step includes the steps of: when all the errorscan be corrected based on the first erasure locator information,generating erasure locator information for erasure error correction ofanother coded data piece using an identical method as the method usedfor generating the first erasure locator information, and when all theerrors can be corrected based on the second erasure locator information,generating erasure locator information for erasure error correction ofanother coded data piece using an identical method as the method usedfor generating the second erasure locator information.
 27. Areproduction method according to claim 25, wherein: the plurality ofsynchronization data pieces include an Nth synchronization data piece,an (N+1) th synchronization data piece, and an (N+2)th synchronizationdata piece, where N is an integer, and the erasure locator informationgeneration step includes the step of, when the synchronization detectioninformation indicates that the Nth synchronization data piece and the(N+2)th synchronization data piece are detected and the (N+1)thsynchronization data piece is not detected, determining at least one ofthe plurality of symbols provided adjacent to the (N+1)thsynchronization data piece as representing erasure.
 28. A reproductionmethod according to claim 25, wherein: the plurality of synchronizationdata pieces include an Nth synchronization data piece and an (N+1)thsynchronization data piece, where N is an integer, and the erasurelocator information generation step includes the step of, when thesynchronization detection information indicates that the (N+1) thsynchronization data piece is detected with a positional offset,determining at least one symbol provided between the Nth synchronizationdata piece and the (N+1)th synchronization data piece as representingerasure.
 29. A reproduction method according to claim 25, wherein theerasure locator information generation step includes the step of, whenthe synchronization detection information indicates that any two or moredata pieces from undetected synchronization data pieces andsynchronization data pieces detected with a positional offset areconsecutive, determining at least one symbol provided between theconsecutive synchronization data pieces as representing erasure.
 30. Areproduction method for reproducing a composite coded data piece from arecording medium having the composite coded data piece recorded thereon,wherein: the composite coded data piece includes a first coded datapiece which is error-correction-coded using a first error correctioncode, a second coded data piece which is error-correction-coded using asecond error correction code having a lower degree of redundancy thanthat of the first error correction code, and a plurality ofsynchronization data pieces, the first coded data piece includes aplurality of first symbols, the second coded data piece includes aplurality of second symbols, at least one first symbol is providedbetween two adjacent synchronization data pieces among the plurality ofsynchronization data pieces, and at least one of the plurality of secondsymbols is provided at least between a synchronization data piece and afirst symbol, the reproduction method comprising: a reading step ofreading the composite coded data piece from the recording medium andoutputting the first coded data piece, the second coded data piece, andthe plurality of synchronization data pieces; a synchronizationdetection information generation step of detecting states of theplurality of synchronization data pieces and generating synchronizationdetection information which represents the detection result; an errorlocation information generation step of performing error correction ofthe first coded data piece and generating error location informationwhich represents an error location of the first coded data; an erasurelocator information generation step of generating at least first erasurelocator information and second erasure locator information whichrepresent an erasure position of the second coded data piece, based onthe error location information and the synchronization detectioninformation: and an erasure error correction step of performing erasureerror correction of the second coded data piece based on at least one ofthe first erasure locator information and the second erasure locatorinformation, wherein the erasure error correction step includes the stepof, when there is an error which cannot be corrected based on the firsterasure locator information, performing erasure error correction of thesecond coded data piece based on the second erasure locator information.31. A reproduction method according to claim 30, wherein: the erasurelocator information generation step includes the steps of: when all theerrors can be corrected based on the first erasure locator information,generating erasure locator information for erasure error correction ofanother second coded data piece using an identical method as the methodused for generating the first erasure locator information, and when allthe errors can be corrected based on the second erasure locatorinformation, generating erasure locator information for erasure errorcorrection of another second coded data piece using an identical methodas the method used for generating the second erasure locatorinformation.
 32. A reproduction method according to claim 30, whereinthe erasure locator information generation step includes the steps of,when the synchronization detection information indicates that there is asynchronization data piece which is not detected and the error locationinformation indicates that no error is detected in the first symbolsimmediately on both sides of the undetected synchronization data piece,determining at least one of the plurality of second symbols providedadjacent to the undetected synchronization data piece as representingerasure.
 33. A reproduction method according to claim 30, wherein: atleast two first symbols are provided between two adjacentsynchronization data pieces among the plurality of synchronization datapieces, at least one second symbol is provided between two adjacentfirst symbols among the at least two first symbols, and the erasurelocator information generation step includes the step of, when the errorlocation information indicates that there is a first symbol detected tohave an error and at least one of the error location information and thesynchronization detection information indicates that one of a detectedsynchronization data piece and a first symbol detected to have no erroris immediately on each of both sides of the first symbol detected tohave an error, determining at least one of the plurality of secondsymbols provided adjacent to the first symbol detected to have an erroras representing erasure.
 34. A reproduction method according to claim30, wherein: the plurality of synchronization data pieces include an Nthsynchronization data piece and an (N+1)th synchronization data piece,where N is an integer, and the erasure locator information generationstep includes the step of, when the synchronization detectioninformation indicates that the (N+1) th synchronization data piece isdetected with a positional offset, determining at least one secondsymbol provided between the Nth synchronization data piece and the(N+1)th synchronization data piece as representing erasure.
 35. Areproduction method according to claim 30, wherein the erasure locatorinformation generation step includes the step of, when thesynchronization detection information indicates that any two or moredata pieces from undetected synchronization data pieces andsynchronization data pieces detected with a positional offset areconsecutive, determining at least one second symbol provided between theconsecutive synchronization data pieces as representing erasure.
 36. Areproduction apparatus for reproducing a composite coded data piece froma recording medium having the composite coded data piece recordedthereon, wherein: the composite coded data piece includes a first codeddata piece which is error-correction-coded using a first errorcorrection code, and a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,the first coded data piece includes a plurality of first symbols, thesecond coded data piece includes a plurality of second symbols, at leastone of the plurality of second symbols is provided between two adjacentfirst symbols of the plurality of first symbols, and the plurality offirst symbols include an Nth first symbol, an (N+1)th first symbol andan (N+2)th first symbol, where N is an integer, the reproductionapparatus comprising: a reading section for reading the composite codeddata piece from the recording medium and outputting the first coded datapiece and the second coded data piece; an error location informationgeneration section for performing error correction of the first codeddata piece and generating error location information which represents anerror location of the first coded data; an erasure locator informationgeneration section for generating erasure locator information whichrepresents an erasure position of the second coded data piece, based onthe error location information; and an erasure error correction sectionfor performing erasure error correction of the second coded data piecebased on the erasure locator information, wherein when the errorlocation information indicates that no error is detected in the Nthfirst symbol and the (N+2)th first symbol and that an error is detectedin the (N+1) th first symbol, the erasure locator information generationsection determines at least one of the plurality of second symbolsprovided adjacent to the (N+1)th first symbol as representing erasure.37. A reproduction apparatus according to claim 36, wherein when theerror location information indicates that no error is detected in theNth first symbol and the (N+2)th first symbol and that an error isdetected in the (N+1)th first symbol, the erasure locator informationgeneration section determines at least one second symbol providedadjacent to the (N+1)th first symbol, among at least one second symbolprovided between the Nth first symbol and the (N+1)th first symbol asrepresenting erasure; and determining at least one second symbolprovided adjacent to the (N+1)th first symbol, among at least one secondsymbol provided between the (N+1)th first symbol and the (N+2)th firstsymbol as representing erasure.
 38. A reproduction apparatus accordingto claim 36, wherein when the error location information indicates thatan error is detected in both of two adjacent first symbols, the erasurelocator information generation section determines all the second symbolsprovided between the two adjacent first symbols as representing erasure.39. A reproduction apparatus for reproducing a composite coded datapiece from a recording medium having the composite coded data piecerecorded thereon, wherein: the composite coded data piece includes afirst coded data piece which is error-correction-coded using a firsterror correction code, and a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,the first coded data piece includes a plurality of first symbols, thesecond coded data piece includes a plurality of second symbols, and atleast two of the plurality of second symbols are provided between twoadjacent first symbols of the plurality of first symbols, thereproduction apparatus comprising: a reading section for reading thecomposite coded data piece from the recording medium and outputting thefirst coded data piece and the second coded data piece; an errorlocation information generation section for performing error correctionof the first coded data piece and generating error location informationwhich represents an error location of the first coded data; an erasurelocator information generation section for generating erasure locatorinformation which represents an erasure position of the second codeddata piece, based on the error location information; and an erasureerror correction section for performing erasure error correction of thesecond coded data piece based on the erasure locator information,wherein when the error location information indicates that a firstsymbol detected to have no error and a first symbol detected to have anerror are adjacent to each other, the erasure locator informationgeneration section determines at least one second symbol providedadjacent to the first symbol detected to have an error, among at leasttwo second symbols provided between the first symbol detected to have noerror and the first symbol detected to have an error, as representingerasure; and determines at least one second symbol provided adjacent tothe first symbol detected to have no error as not representing erasure.40. A reproduction apparatus according to claim 39, wherein when theerror location information indicates that an error is detected in bothof two adjacent first symbols, the erasure locator informationgeneration section determines all the second symbols provided betweenthe two adjacent first symbols as representing erasure.
 41. Areproduction apparatus for reproducing a coded data piece from arecording medium having a plurality of synchronization data pieces andthe coded data piece which is error-correction-coded recorded thereon,wherein: the coded data piece includes a plurality of symbols, at leastone of the plurality of symbols is provided between two adjacentsynchronization data pieces among the plurality of synchronization datapieces, and the plurality of synchronization data pieces include an Nthsynchronization data piece, an (N+1)th synchronization data piece, andan (N+2)th synchronization data piece, where N is an integer, thereproduction apparatus comprising: a reading section for reading theplurality of synchronization data pieces and the coded data piece fromthe recording medium; a synchronization detection information generationsection for detecting states of the plurality of synchronization datapieces and generating synchronization detection information whichrepresents the detection result; an erasure locator informationgeneration section for generating erasure locator information whichrepresents an erasure position of the coded data piece, based on thesynchronization detection information; and an erasure error correctionsection for performing erasure error correction of the coded data piecebased on the erasure locator information, wherein when thesynchronization detection information indicates that the Nthsynchronization data piece and the (N+2)th synchronization data pieceare detected and the (N+1)th synchronization data piece is not detected,the erasure locator information generation section determines at leastone of the plurality of symbols provided adjacent to the (N+1)thsynchronization data piece as representing erasure.
 42. A reproductionapparatus according to claim 41, wherein when the synchronizationdetection information indicates that the Nth synchronization data pieceand the (N+2)th synchronization data piece are detected and the (N+1)thsynchronization data piece is not detected, the erasure locatorinformation generation section determines at least one symbol providedadjacent to the (N+1)th synchronization data piece, among at least onesymbol provided between the Nth synchronization data piece and the(N+1)th synchronization data piece as representing erasure; anddetermines at least one symbol provided adjacent to the (N+1)thsynchronization data piece, among at least one symbol provided betweenthe (N+1)th synchronization data piece and the (N+2)th synchronizationdata piece as representing erasure.
 43. A reproduction apparatusaccording to claim 41, wherein when the synchronization detectioninformation indicates that neither of the two adjacent synchronizationdata pieces are detected, the erasure locator information generationsection determines all the symbols provided between the two undetectedsynchronization data pieces as representing erasure.
 44. A reproductionapparatus for reproducing a coded data piece from a recording mediumhaving a plurality of synchronization data pieces and the coded datapiece which is error-correction-coded recorded thereon, wherein: thecoded data piece includes a plurality of symbols, and at least two ofthe plurality of symbols are provided between two adjacentsynchronization data pieces of the plurality of synchronization datapieces, the reproduction apparatus comprising: a reading section forreading the plurality of synchronization data pieces and the coded datapiece from the recording medium; a synchronization detection informationgeneration section for detecting states of the plurality ofsynchronization data pieces and generating synchronization detectioninformation which represents the detection result; an erasure locatorinformation generation section for generating erasure locatorinformation which represents an erasure position of the coded datapiece, based on the synchronization detection information; and anerasure error correction section for performing erasure error correctionof the coded data piece based on the erasure locator information,wherein when the synchronization detection information indicates that asynchronization data piece adjacent to a detected synchronization datapiece is not detected, the erasure locator information generationsection determines at least one symbol provided adjacent to theundetected synchronization data piece, among at least two symbolsprovided between the detected synchronization data piece and theundetected synchronization data piece, as representing erasure; anddetermines at least one symbol provided adjacent to the detectedsynchronization data piece as not representing erasure.
 45. Areproduction apparatus according to claim 44, wherein when thesynchronization detection information indicates that neither of the twoadjacent synchronization data pieces are detected, the erasure locatorinformation generation section determines all the symbols providedbetween the two undetected synchronization data pieces as representingerasure.
 46. A reproduction apparatus for reproducing a composite codeddata piece from a recording medium having the composite coded data piecerecorded thereon, wherein: the composite coded data piece includes afirst coded data piece which is error-correction-coded using a firsterror correction code, a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,and a plurality of synchronization data pieces, the first coded datapiece includes a plurality of first symbols, the second coded data pieceincludes a plurality of second symbols, at least one first symbol isprovided between two adjacent synchronization data pieces among theplurality of synchronization data pieces, and at least one of theplurality of second symbols is provided at least between asynchronization data piece and a first symbol, the reproductionapparatus comprising: a reading section for reading the composite codeddata piece from the recording medium and outputting the first coded datapiece, the second coded data piece, and the plurality of synchronizationdata pieces; a synchronization detection information generation sectionfor detecting states of the plurality of synchronization data pieces andgenerating synchronization detection information which represents thedetection result; an error location information generation section forperforming error correction of the first coded data piece and generatingerror location information which represents an error location of thefirst coded data; an erasure locator information generation section forgenerating erasure locator information which represents an erasureposition of the second coded data piece, based on the error locationinformation and the synchronization detection information; and anerasure error correction section for performing erasure error correctionof the second coded data piece based on the erasure locator information,wherein when the synchronization detection information indicates thatthere is a synchronization data piece which is not detected and theerror location information indicates that no error is detected in thefirst symbols immediately on both sides of the undetectedsynchronization data piece, the erasure locator information generationsection determines at least one of the plurality of second symbolsprovided adjacent to the undetected synchronization data piece asrepresenting erasure.
 47. A reproduction apparatus according to claim46, wherein: at least two first symbols are provided between twoadjacent synchronization data pieces among the plurality ofsynchronization data pieces, at least one second symbol is providedbetween two adjacent first symbols among the at least two first symbols,and when the error location information indicates that there is a firstsymbol detected to have an error and at least one of the error locationinformation and the synchronization detection information indicates thatone of a detected synchronization data piece and a first symbol detectedto have no error is immediately on each of both sides of the firstsymbol detected to have an error, the erasure locator informationgeneration section determines at least one of the plurality of secondsymbols provided adjacent to the first symbol detected to have an erroras representing erasure.
 48. A reproduction apparatus for reproducing acoded data piece from a recording medium having a plurality ofsynchronization data pieces and the coded data piece which iserror-correction-coded recorded thereon, wherein: the coded data pieceincludes a plurality of symbols, at least one of the plurality ofsymbols is provided between two adjacent synchronization data piecesamong the plurality of synchronization data pieces, and the plurality ofsynchronization data pieces include an Nth synchronization data pieceand an (N+1)th synchronization data piece, where N is an integer, thereproduction apparatus comprising: a reading section for reading theplurality of synchronization data pieces and the coded data piece fromthe recording medium; a synchronization detection information generationsection for detecting states of the plurality of synchronization datapieces and generating synchronization detection information whichrepresents the detection result; an erasure locator informationgeneration section for generating erasure locator information whichrepresents an erasure position of the coded data piece, based on thesynchronization detection information; and an erasure error correctionsection for performing erasure error correction of the coded data piecebased on the erasure locator information, wherein when thesynchronization detection information indicates that the (N+1) thsynchronization data piece is detected with a positional offset, theerasure locator information generation section determines at least onesymbol provided between the Nth synchronization data piece and the(N+1)th synchronization data piece as representing erasure.
 49. Areproduction apparatus according to claim 48, wherein: the plurality ofsynchronization data pieces include an (N+2)th synchronization datapiece, and when the synchronization detection information indicates thatthe (N+1)th synchronization data piece is detected with a positionaloffset, the erasure locator information generation section determines atleast one symbol provided between the (N+1)th synchronization data pieceand the (N+2)th synchronization data piece as not representing erasure.50. A reproduction apparatus for reproducing a composite coded datapiece from a recording medium having the composite coded data piecerecorded thereon, wherein: the composite coded data piece includes afirst coded data piece which is error-correction-coded using a firsterror correction code, a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,and a plurality of synchronization data pieces, the first coded datapiece includes a plurality of first symbols, the second coded data pieceincludes a plurality of second symbols, at least one first symbol isprovided between two adjacent synchronization data pieces among theplurality of synchronization data pieces, at least one of the pluralityof second symbols is provided at least between a synchronization datapiece and a first symbol, and the plurality of synchronization datapieces include an Nth synchronization data piece and an (N+1)thsynchronization data piece, where N is an integer, the reproductionapparatus comprising: a reading section for reading the composite codeddata piece from the recording medium and outputting the first coded datapiece, the second coded data piece, and the plurality of synchronizationdata pieces; a synchronization detection information generation sectionfor detecting states of the plurality of synchronization data pieces andgenerating synchronization detection information which represents thedetection result; an error location information generation section forperforming error correction of the first coded data piece and generatingerror location information which represents an error location of thefirst coded data; an erasure locator information generation section forgenerating erasure locator information which represents an erasureposition of the second coded data piece, based on the error locationinformation and the synchronization detection information; and anerasure error correction section for performing erasure error correctionof the second coded data piece based on the erasure locator information,wherein when the synchronization detection information indicates thatthe (N+1)th synchronization data piece is detected with a positionaloffset, the erasure locator information generation section determines atleast one second symbol provided between the Nth synchronization datapiece and the (N+1)th synchronization data piece as representingerasure.
 51. A reproduction apparatus according to claim 50, wherein:the plurality of synchronization data pieces include an (N+2)thsynchronization data piece, and when the synchronization detectioninformation indicates that the (N+1)th synchronization data piece isdetected with a positional offset, the erasure locator informationgeneration section determines at least one second symbol providedbetween the (N+1)th synchronization data piece and the (N+2)thsynchronization data piece as not representing erasure.
 52. Areproduction apparatus for reproducing a composite coded data piece froma recording medium having the composite coded data piece recordedthereon, wherein: the composite coded data piece includes a first codeddata piece which is error-correction-coded using a first errorcorrection code, a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,and a plurality of synchronization data pieces, the first coded datapiece includes a plurality of first symbols, the second coded data pieceincludes a plurality of second symbols, at least one first symbol isprovided between two adjacent synchronization data pieces among theplurality of synchronization data pieces, at least one of the pluralityof second symbols is provided at least between a synchronization datapiece and a first symbol, the plurality of synchronization data piecesinclude an Nth synchronization data piece and an (N+1)th synchronizationdata piece, where N is an integer, and a prescribed first symbol isprovided between the Nth synchronization data piece and the (N+1)thsynchronization data piece, the reproduction apparatus comprising: areading section for reading the composite coded data piece from therecording medium and outputting the first coded data piece, the secondcoded data piece, and the plurality of synchronization data pieces; asynchronization detection information generation section for detectingstates of the plurality of synchronization data pieces and generatingsynchronization detection information which represents the detectionresult; an error location information generation section for performingerror correction of the first coded data piece and generating errorlocation information which represents an error location of the firstcoded data; an erasure locator information generation section forgenerating erasure locator information which represents an erasureposition of the second coded data piece, based on the error locationinformation and the synchronization detection information; and anerasure error correction section for performing erasure error correctionof the second coded data piece based on the erasure locator information,wherein when the synchronization detection information indicates thatthe (N+1)th synchronization data piece is detected with a positionaloffset, the erasure locator information generation section determines atleast one second symbol provided between the prescribed first symbol andthe (N+1)th synchronization data piece as representing erasure.
 53. Areproduction apparatus according to claim 52, wherein: the plurality ofsynchronization data pieces include an (N+2)th synchronization datapiece, another prescribed first symbol is provided between the (N+1)thsynchronization data piece and the (N+2)th synchronization data piece,and when the synchronization detection information indicates that the(N+1)th synchronization data piece is detected with a positional offset,the erasure locator information generation section determines at leastone second symbol provided between the (N+1)th synchronization datapiece and the another prescribed first symbol as not representingerasure.
 54. A reproduction apparatus for reproducing a coded data piecefrom a recording medium having a plurality of synchronization datapieces and the coded data piece which is error-correction-coded recordedthereon, wherein: the coded data piece includes a plurality of symbols,and at least one of the plurality of symbols is provided between twoadjacent synchronization data pieces of the plurality of synchronizationdata pieces, the reproduction apparatus comprising: a reading sectionfor reading the plurality of synchronization data pieces and the codeddata piece from the recording medium; a synchronization detectioninformation generation section for detecting states of the plurality ofsynchronization data pieces and generating synchronization detectioninformation which represents the detection result; an erasure locatorinformation generation section for generating erasure locatorinformation which represents an erasure position of the coded datapiece, based on the synchronization detection information; and anerasure error correction section for performing erasure error correctionof the coded data piece based on the erasure locator information,wherein when the synchronization detection information indicates thatany two or more data pieces from undetected synchronization data piecesand synchronization data pieces detected with a positional offset areconsecutive, the erasure locator information generation sectiondetermines at least one symbol provided between the consecutivesynchronization data pieces as representing erasure.
 55. A reproductionapparatus for reproducing a composite coded data piece from a recordingmedium having the composite coded data piece recorded thereon, wherein:the composite coded data piece includes a first coded data piece whichis error-correction-coded using a first error correction code, a secondcoded data piece which is error-correction-coded using a second errorcorrection code having a lower degree of redundancy than that of thefirst error correction code, and a plurality of synchronization datapieces, the first coded data piece includes a plurality of firstsymbols, the second coded data piece includes a plurality of secondsymbols, at least one first symbol is provided between two adjacentsynchronization data pieces among the plurality of synchronization datapieces, and at least one of the plurality of second symbols is providedat least between a synchronization data piece and a first symbol, thereproduction apparatus comprising: a reading section for reading thecomposite coded data piece from the recording medium and outputting thefirst coded data piece, the second coded data piece, and the pluralityof synchronization data pieces; a synchronization detection informationgeneration section for detecting states of the plurality ofsynchronization data pieces and generating synchronization detectioninformation which represents the detection result; an error locationinformation generation section for performing error correction of thefirst coded data piece and generating error location information whichrepresents an error location of the first coded data; an erasure locatorinformation generation section for generating erasure locatorinformation which represents an erasure position of the second codeddata piece, based on the error location information and thesynchronization detection information; and an erasure error correctionsection for performing erasure error correction of the second coded datapiece based on the erasure locator information, wherein when thesynchronization detection information indicates that any two or moredata pieces from undetected synchronization data pieces andsynchronization data pieces detected with a positional offset areconsecutive, the erasure locator information generation sectiondetermines at least one second symbol provided between the consecutivesynchronization data pieces as representing erasure.
 56. A reproductionapparatus according to claim 55, wherein the erasure locator informationgeneration section determines at least one first symbol provided betweenthe consecutive synchronization data pieces as representing erasure. 57.A reproduction apparatus for reproducing a composite coded data piecefrom a recording medium having the composite coded data piece recordedthereon, wherein: the composite coded data piece includes a first codeddata piece which is error-correction-coded using a first errorcorrection code, and a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,the first coded data piece includes a plurality of first symbols, thesecond coded data piece includes a plurality of second symbols, and atleast one of the plurality of second symbols is provided between twoadjacent first symbols of the plurality of first symbols, thereproduction apparatus comprising: a reading section for reading thecomposite coded data piece from the recording medium and outputting thefirst coded data piece and the second coded data piece; an errorlocation information generation section for performing error correctionof the first coded data piece and generating error location informationwhich represents an error location of the first coded data; an erasurelocator information generation section for generating at least firsterasure locator information and second erasure locator information whichrepresent an erasure position of the second coded data piece, based onthe error location information; and an erasure error correction sectionfor performing erasure error correction of the second coded data piecebased on at least one of the first erasure locator information and thesecond erasure locator information, wherein when there is an error whichcannot be corrected based on the first erasure locator information, theerasure error correction section performs erasure error correction ofthe second coded data piece based on the second erasure locatorinformation.
 58. A reproduction apparatus according to claim 57,wherein: when all the errors can be corrected based on the first erasurelocator information, the erasure locator information generation sectiongenerates erasure locator information for erasure error correction ofanother second coded data piece using an identical method as the methodused for generating the first erasure locator information, and when allthe errors can be corrected based on the second erasure locatorinformation, the erasure locator information generation sectiongenerates erasure locator information for erasure error correction ofanother second coded data piece using an identical method as the methodused for generating the second erasure locator information.
 59. Areproduction apparatus according to claim 57, wherein: the plurality offirst symbols include an Nth first symbol, an (N+1)th first symbol andan (N+2)th first symbol, where N is an integer, and when the errorlocation information indicates that no error is detected in the Nthfirst symbol and the (N+2)th first symbol and that an error is detectedin the (N+1)th first symbol, the erasure locator information generationsection determines at least one of the plurality of second symbolsprovided adjacent to the (N+1)th first symbol as representing erasure.60. A reproduction apparatus for reproducing a coded data piece from arecording medium having a plurality of synchronization data pieces andthe coded data piece which is error-correction-coded recorded thereon,wherein: the coded data piece includes a plurality of symbols, and atleast one of the plurality of symbols is provided between two adjacentsynchronization data pieces among the plurality of synchronization datapieces, the reproduction apparatus comprising: a reading section forreading the plurality of synchronization data pieces and the coded datapiece from the recording medium; a synchronization detection informationgeneration section for detecting states of the plurality ofsynchronization data pieces and generating synchronization detectioninformation which represents the detection result; an erasure locatorinformation generation section for generating at least first erasurelocator information and second erasure locator information whichrepresent an erasure position of the coded data piece, based on thesynchronization detection information; and an erasure error correctionsection for performing erasure error correction of the coded data piecebased on at least one of the first erasure locator information and thesecond erasure locator information, wherein when there is an error whichcannot be corrected based on the first erasure locator information, theerasure error correction section performs erasure error correction ofthe coded data piece based on the second erasure locator information.61. A reproduction apparatus according to claim 60, wherein: when allthe errors can be corrected based on the first erasure locatorinformation, the erasure locator information generation sectiongenerates erasure locator information for erasure error correction ofanother coded data piece using an identical method as the method usedfor generating the first erasure locator information, and when all theerrors can be corrected based on the second erasure locator information,the erasure locator information generation section generates erasurelocator information for erasure error correction of another coded datapiece using an identical method as the method used for generating thesecond erasure locator information.
 62. A reproduction apparatusaccording to claim 60, wherein: the plurality of synchronization datapieces include an Nth synchronization data piece, an (N+1)thsynchronization data piece, and an (N+2) th synchronization data piece,where N is an integer, and when the synchronization detectioninformation indicates that the Nth synchronization data piece and the(N+2)th synchronization data piece are detected and the (N+1)thsynchronization data piece is not detected, the erasure locatorinformation generation section determines at least one of the pluralityof symbols provided adjacent to the (N+1)th synchronization data pieceas representing erasure.
 63. A reproduction apparatus according to claim60, wherein: the plurality of synchronization data pieces include an Nthsynchronization data piece and an (N+1)th synchronization data piece,where N is an integer, and when the synchronization detectioninformation indicates that the (N+1)th synchronization data piece isdetected with a positional offset, the erasure locator informationgeneration section determines at least one symbol provided between theNth synchronization data piece and the (N+1)th synchronization datapiece as representing erasure.
 64. A reproduction apparatus according toclaim 60, wherein: when the synchronization detection informationindicates that any two or more data pieces from undetectedsynchronization data pieces and synchronization data pieces detectedwith a positional offset are consecutive, the erasure locatorinformation generation section determines at least one symbol providedbetween the consecutive synchronization data pieces as representingerasure.
 65. A reproduction apparatus for reproducing a composite codeddata piece from a recording medium having the composite coded data piecerecorded thereon, wherein: the composite coded data piece includes afirst coded data piece which is error-correction-coded using a firsterror correction code, a second coded data piece which iserror-correction-coded using a second error correction code having alower degree of redundancy than that of the first error correction code,and a plurality of synchronization data pieces, the first coded datapiece includes a plurality of first symbols, the second coded data pieceincludes a plurality of second symbols, at least one first symbol isprovided between two adjacent synchronization data pieces among theplurality of synchronization data pieces, and at least one of theplurality of second symbols is provided at least between asynchronization data piece and a first symbol, the reproductionapparatus comprising: a reading section for reading the composite codeddata piece from the recording medium and outputting the first coded datapiece, the second coded data piece, and the plurality of synchronizationdata pieces; a synchronization detection information generation sectionfor detecting states of the plurality of synchronization data pieces andgenerating synchronization detection information which represents thedetection result; an error location information generation section forperforming error correction of the first coded data piece and generatingerror location information which represents an error location of thefirst coded data; an erasure locator information generation section forgenerating at least first erasure locator information and second erasurelocator information which represent an erasure position of the secondcoded data piece, based on the error location information and thesynchronization detection information; and an erasure error correctionsection for performing erasure error correction of the second coded datapiece based on at least one of the first erasure locator information andthe second erasure locator information, wherein when there is an errorwhich cannot be corrected based on the first erasure locatorinformation, the erasure error correction section performs erasure errorcorrection of the second coded data piece based on the second erasurelocator information.
 66. A reproduction apparatus according to claim 65,wherein: when all the errors can be corrected based on the first erasurelocator information, the erasure locator information generation sectiongenerates erasure locator information for erasure error correction ofanother second coded data piece using an identical method as the methodused for generating the first erasure locator information, and when allthe errors can be corrected based on the second erasure locatorinformation, the erasure locator information generation sectiongenerates erasure locator information for erasure error correction ofanother second coded data piece using an identical method as the methodused for generating the second erasure locator information.
 67. Areproduction apparatus according to claim 65, wherein: when thesynchronization detection information indicates that there is asynchronization data piece which is not detected and the error locationinformation indicates that no error is detected in the first symbolsimmediately on both sides of the undetected synchronization data piece,the erasure locator information generation section determines at leastone of the plurality of second symbols provided adjacent to theundetected synchronization data piece as representing erasure.
 68. Areproduction apparatus according to claim 65, wherein: at least twofirst symbols are provided between two adjacent synchronization datapieces among the plurality of synchronization data pieces, at least onesecond symbol is provided between two adjacent first symbols among theat least two first symbols, and when the error location informationindicates that there is a first symbol detected to have an error and atleast one of the error location information and the synchronizationdetection information indicates that one of a detected synchronizationdata piece and a first symbol detected to have no error is immediatelyon each of both sides of the first symbol detected to have an error, theerasure locator information generation section determines at least oneof the plurality of second symbols provided adjacent to the first symboldetected to have an error as representing erasure.
 69. A reproductionapparatus according to claim 65, wherein: the plurality ofsynchronization data pieces include an Nth synchronization data pieceand an (N+1)th synchronization data piece, where N is an integer, andwhen the synchronization detection information indicates that the(N+1)th synchronization data piece is detected with a positional offset,the erasure locator information generation section determines at leastone second symbol provided between the Nth synchronization data pieceand the (N+1)th synchronization data piece as representing erasure. 70.A reproduction apparatus according to claim 65, wherein: when thesynchronization detection information indicates that any two or moredata pieces from undetected synchronization data pieces andsynchronization data pieces detected with a positional offset areconsecutive, the erasure locator information generation sectiondetermines at least one second symbol provided between the consecutivesynchronization data pieces as representing erasure.